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At this time a combination of circumstances occurred which gave a great stimulus to rubber planting in the Orient. A deadly rust disease of coffee (Hemileia vastatrix Berk. and Br.) completely ruined the coffee plantations of that part of the world, and the planters in desperation were seeking a substitute crop. Rubber, as one of the most promising crops, engaged their attention, and soon large acreages were planted with Hevea brasiliensis.

In a few years considerable plantation rubber appeared on the market and, in spite of the early skepticism of the manufacturers, continued to be produced in larger and larger quantities. Improved methods of preparation gradually removed most of the objections to its use, until now it is considered the equal of fine hard Para, long the highest quality of rubber known.

With the passage of years many types of rubber disappeared completely, either because of the exhaustion of their sources or the decline in price which made their production unprofitable. Plantation rubber has constantly assumed larger proportions in the world's markets, while wild rubber has steadily become of less importance, until plantation rubber has come to control the situation completely. Wild rubber is now obtained from relatively few plants, and unless certain special uses demand certain types the exploitation of the wild product must soon cease altogether.

The United States is now the largest consumer of rubber, while the plantation-rubber industry is centered in the Orient, in India, Ceylon, Burma, the Federated Malay States, the Straits Settlements, Sumatra, Java, and Borneo. This wide separation of consumer from source of supply has given concern to many, who have pointed out the need of sources of supply nearer home which could be drawn upon in case the more distant sources were cut off by war.

In addition to this, the control of this raw product, so vastly important in our transportation system, by foreign powers was emphasized by a recent restriction act which aims at the control of the price of rubber. These and other considerations led to the initiation in 1923 of a series of investigations of the sources of crude-rubber supply undertaken by the United States Department of Agriculture and the United States Department of Commerce. This report embodies the results of one of the investigations conducted by the United States Department of Agriculture.

PURPOSE OF THE EXPEDITION

An expedition was sent to Para, Brazil, in July, 1923, to make a study of the botanical phases of the rubber industry on the banks of the Amazon and its tributaries. The problems to be investigated may be stated as follows:

(1) The general status of the rubber industry in the Amazon region at the present time, including a study of present methods of production and the possibility of improving them.

(2) The rubber resources of the region available in case of a crisis and the means of making such resources available.

(3) The suitability of the region for the cultivation of rubber, especially as determined by the growth and development of the trees.

(4) The types of Hevea and the possibility of securing more desirable strains for plantation use in the Amazon Valley or elsewhere.

(5) The prevalence of diseases of Hevea and plant pathological conditions generally.

PERSONNEL OF THE EXPEDITION

The expedition from the United States Department of Agriculture was composed of Carl D. La Rue, specialist in rubber investigations, in charge of the party; James R. Weir, pathologist in rubber investigations; and E. L. Prizer, field assistant, and Morris K. Jessup, field assistant, who did the photographic work for the party.

In Para the party joined forces with another from the United States Department of Commerce, and to collaborate with these American investigators the Brazilian Government appointed a commission consisting of Hannibal Porto, chief; Avellino Olivera, geologist and later chief of the commission; Gerardo A. Kuhlman, botanist; Raymundo Monteiro da Costa, rubber specialist; and Fernando Solidade, physician.

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FIG. 1.-The Andirá, the boat which was chartered and equipped by the Brazilian Government for the use of the three expeditionary parties. The Andirá is a fine example of the type of boat common on the Amazon and its tributaries

ITINERARY

The Brazilian Government had chartered and equipped a commodious and comfortable river boat, the Andirá (fig. 1), for the use of the American and Brazilian investigators, and on this they proceeded to Manaos and later to Porto Velho, the limit of navigation on the Madeira River. From this point the Madeira-Mamore Railway carried the travelers to Guajara Mirim, on the Mamore River, whence they proceeded by batelaões (broad-bottomed strongly built river boats) and canoes up the Mamore to the Pacanova River, thence up this to the Ouro Preto River, and finally for a distance up the Ouro Preto into the jungles of Matto Grosso. From Matto Grosso the party returned to Villa Murtinho at the mouth of the Rio Beni, which stream they ascended to Riberalta and from that

point continued up the Madre de Dios to Sena. When the party returned by river and rail to Abuna at the mouth of the river of that name a division of the party was made; the Brazilian and Commerce parties ascended the Abuna into the Acre Territory and crossed overland to the Rio Acre, while the Agriculture party came back to the Andirá at Porto Velho and returned on that boat to Manaos and later to Para.

At Para Doctor Weir was transferred from the rubber investigations to other work and proceeded to Rio de Janeiro and Buenos Aires before returning to New York. Prizer and Jessup returned to Washington, while the writer sailed for Cobija, in the Acre Territory of Bolivia, by way of the Amazon, Purus, and Acre Rivers. The return journey was made over the same route.

THE GENUS HEVEA

Mention has already been made of the fact that La Condamine (13) was the first scientist to take note of the rubber tree and its strange product and that he published (14) the description and drawings of a Hevea tree submitted to him by Fresneau, which are the earliest extant. It is most likely that the rubber which La Condamine first saw in the Province of Esmeraldas did not come from a tree of Hevea but from some species of Castilla, but Fresneau's drawings and descriptions, imperfect as they are, undoubtedly refer to some species of Hevea.

Fusée Aublet (4) in 1775 established the genus Hevea with Hevea guianensis as the type species. The name "Hevea" he derived from Hevé, which he says is the Carib name for the tree. Plate 335 of Aublet's work is labeled Hevea peruviana for some reason, but is really H. guianensis.

Since the time of Aublet certain species of the genus have been known by a number of different generic names, such as Siphonia, Caoutschoua, Siphonanthus, Jatropha, and Micrandra; but Hevea has finally been firmly established as the proper generic designation. Spruce (41) in his long sojourn on the Amazon assembled a considerable number of species of Hevea, among which are found Hevea spruceana Muell. Arg., H. discolor Muell. Arg., H. membranacea Muell. Arg., H. pauciflora Muell. Arg., H. rigidifolia Muell. Arg., H. benthamiana Muell. Arg., H. lutea Muell. Arg., and H. brasiliensis Muell. Arg.

Martius (27) and Richard Schomburgk (36) also collected species of this genus; in more recent times Ule (42), Huber (9, 10, 11), and Ducke have been active in this work.

In 1873-74 volume 11 of Flora Brasiliensis by Martius (27) appeared, consisting of the Euphorbiace treated by Mueller ArgoIn this the following 11 species of Hevea were recognized:

Hevea spruceana Muell. Arg.

Siphonia spruceana Benth.
H. discolor Muell. Arg.

Micrandra ternata R. Brown.
Siphonia discolor Benth.
H. membranacea Muell. Arg.
H. pauciflora Muell. Arg.

Siphonia pauciflora Benth.
H. rigidifolia Muell. Arg.

Siphonia rigidifolia Benth. H. nitida Muell. Arg.

H. benthamiana Muell. Arg.
H. lutea Muell. Arg.

Siphonia lutea Benth.
H. brasiliensis Muell. Arg.
Siphonia brasiliensis Kunth.
H. janeirensis Muell. Arg.
H. guianensis Aubl.

Jatropha elastica Linn.
Siphonia elastica Pers.
Siphonia cahuchu Willd.

Pax (31), in Engler's Pflanzenreich, recognized the following species:

Hevea benthamiana Muell. Arg.

H. discolor Spruce.

H. duckei Huber.

H. nitida Muell. Arg.

H. paludosa Ule.

H. brasiliensis (H. B. K.) Muell.

var. janeirensis (Muell. Arg.) Pax.
H. janeirensis Muell. Arg.
H. sieberi Warburg.

Siphonia brasiliensis H. B. K.

var. stylosa Huber.

var. cuneata (Huber) Pax.

H. lutea var. cuneata Huber.
H. cuneata Huber.

H. sp. "itauba" Ule.

H. peruviana Lechler ex Huber.
var. randiana (Huber) Pax.
H. lutea (Benth.) Muell. Arg.
H. apiculata Baill.

H. lutea var. apiculata Muell. Arg.
H. peruviana Lechler ex Benth.
Siphonia lutea Benth.

Siphonia apiculata Spruce ex Baill.
H. rigidifolia (Benth.) Muell. Arg.
Siphonia rigidifolia Spruce.

H. spruceana (Benth.) Muell. Arg.
Siphonia spruceana Benth.

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Pax pointed out the great difficulty encountered in delimiting species of Hevea with such material as is available, which in the case of only a few species consists of specimens of leaves, flowers, and fruits and even in some of these offers no certainty that the different structures are derived from the same source. Pax decried the practice (to which he feels Huber was especially addicted) of describing species from leaf specimens only.

Huber (9, 11) recognized 24 species in the genus, which are listed below:

Hevea guianensis Aubl.
H. nigra Ule.

H. apiculata Baill.

H. cuneata Hub.

H. peruviana Lechler.

H. benthamiana Muell. Arg.

H. duckei Hub.

H. paludosa Ule.

H. rigidifolia Muell. Arg.

H. minor Hemsley.

H. microphylla Ule.

H. randiana Hub.

H. brasiliensis Muell. Arg.

var. stylosa Hub.

H. spruceana Muell. Arg.

var. tridentata Hub.
H. similis Hemsley.
H. discolor Muell. Arg.

H. confusa Hemsley.

H. pauciflora Muell. Arg.
H. nitida Muell. Arg.

H. viridis Huber.

H. kunthiana (Baill.) Huber.
H. foxii Huber.

H. glabrescens Huber.

H. lutea Muell. Arg.

From an examination of the type material in the Museu Goeldi of a number of Huber's species, the writer is inclined to believe that Huber, although in all probability better acquainted with the genus Hevea than any other botanist, was too much inclined to describe species from inadequate material and to base them on rather small and not certainly constant differences.

A satisfactory revision of the genus can not be made until more extensive collections than are now available have been assembled. Flowers, or fruit, or both are lacking in too many type specimens.

But such extensive collections are not likely to be made in the near future. The genus is widely spread over a sparsely settled country which contains few people with sufficient scientific interest to induce them to make botanical collections. Spruce (40) long ago pointed out the difficulty encountered in collecting specimens from Hevea trees 100 to 125 feet high, which no native can be induced to climb and which cost much time and much money to fell. The writer can testify that Spruce did not exaggerate the obstacles.

As things stand at present, it is by no means impossible that certain species differing little from other related species may represent merely fluctuating variations and may not be constant at all. Material from a single collection can tell nothing conclusive about such things. The writer's experience (17) with Hevea trees on plantations in the Orient, especially in Sumatra, shows that the trees there display a great range of variation in their characters. In this case we are dealing with Hevea brasiliensis, though we must admit the possibility that the oriental race may represent some admixture with other species, such as H. collina. Huber (10) is inclined to doubt the hybridization, as does the writer. Also it may be found that the cultivated species is more variable than it was in nature. The common notion that cultivation induces variation has been attacked in recent years, although its possibility is admitted here. But if other species in Brazil are anything like as variable as H. brasiliensis in the East, we need to be very sure of the stability of the characters used for species delimitation.

Where differences are known to be constant, their extent is not of such great importance. As in other groups of plants, the determination of a difference as specific or only varietal will largely depend upon the measuring stick used by any given student of the group. For example, it does not much matter whether we consider H. randiana Huber a separate species or with Pax reduce it to H. brasiliensis var. randiana (Huber) Pax, but it does matter greatly whether or not we know that its deviations from H. brasiliensis are constant and heritable.

GEOGRAPHICAL DISTRIBUTION

The results of this expedition add very little to our knowledge of the geographic distribution of the species of Hevea. Ule (42) discussed the distribution of the different species and published a map showing the entire range of the genus. He stated that the area of distribution is divided by the Equator into a northern region through which rivers of black waters flow and a southern region drained by rivers of white water. The northern region he reported as containing H. quianensis, H. collina, H. benthamiana, H. duckei, H. rigidifolia, H. discolor, H. minor, H. pauciflora, H. membranacea, H. microphylla, and H. lutea, 11 species in all.

The southern area, he said, was inhabited by H. guianensis, H. nigra, H. brasiliensis, H. nitida, H. paludosa, H. spruceana, and H. similis, seven species.

Huber (11) points out that the Equator does not represent the division between the black-water rivers and those with white water; even the Rio Negro lies south of the Equator. The area north of the Equator contains, according to Huber, H. guianensis, H. benthamiana, H. rigidifolia, H. microphylla, H. minor, H. pauciflora, H.

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