like Puccinia spores, but have, in the European species,

generally two germ-pores in each cell, and these are placed

队

m

Fig. 3.-Chrysomyxa rhododendri. Section of spore-bed showing the compound teleutospores (a), one of which is in the act of germination, having emitted a promycelium () from upper corner of its superior compartment. In most of the other spores germination has commenced. e, The epidermal cells of the host-plant (R. hirsutum); m, mycelial hypha. (De Bary.)

at that end of the cell which is nearest the septum (Plate III. Figs. 22, 23; and Plate IV. Figs. 11, 13, and 14).

Germination.-The period at which germination takes place in teleutospores is subject to variation with the different species of Uredines. In the greater number of cases this process ensues only after the teleutospore has remained for some considerable time in a state of quiescence or rest. Generally this resting period extends from the summer or autumn of one year until the ensuing spring, corresponding, in fact, with the conditions of the host-plant, which of course, in the case of deciduous plants, is without suitable foliage during the winter months into which the fungus can gain an entrance. On the other hand, there are several species in which teleutospores germinate as soon as they are mature, without undergoing any resting period (Leptopuccinia, Lepturomyces); while there are others which have only a very short resting period (P. rubigo

vera, poarum). In either case the germinative process is the same. This consists in the protrusion of a germ-tube from the teleutospore through the germ-pore above mentioned, which tube is really an extension of the endospore through the germ-pore. This tube consists of a hyaline, homogeneous membrane, into which the protoplasm contained within the spore passes. This tube (the promycelium) does not, like the germ-tubes of the uredospores and æcidiospores, elongate indefinitely, but, after attaining a certain length, ceases to grow onwards and terminates in a blind, blunt extremity. Into the promycelial tube the protoplasm passes from the spore, and accumulates towards the peripheral extremity, so that the end nearest the spore becomes empty. The distal end now exhibits one or more septa, which are formed from above downwards. At the same time, from each compartment thus divided off there arises a single, short, pointed branch; these at their points dilate. The dilated end becomes the receptacle for the protoplasm originally contained in each compartment, and rapidly assumes an oval or subreniform outline (the promycelial spore), which in the course of a few hours becomes abstricted and falls off (Plate IV. Figs. 2-10). The promycelial spores, when placed in water or upon any damp surface, forthwith germinate (Plate III. Fig. 24). This process consists in the outgrowth, from some point of their surface, of a short but acutely pointed tube. Placed upon the cuticle of a living leaf of the proper host-plant, this germ-tube turns its point downwards, and, piercing the epidermal cell-walls, enters the tissue of the leaf (Plate IV. Fig. 1). Having thus gained an entry into its host, the protoplasm contained in the promycelial spore passes downwards into the germ-tube, leaving the spore empty. The empty spore-cell falls off, and the minute opening through which the germ-tube has entered the epidermal cell ceases

to be visible; this is probably due to the elasticity of the epidermal cell-wall. The germ-tube itself continues its onward growth; soon branching, it insinuates itself between the cells of the host, where it gives rise to a mycelial development, similar to that which arises from the acidiospore or uredospore germ-tubes.

With the Leptopuccinia and Lepturomyces, the germtube of the promycelial spore does not bore its way through the epidermal cells, but enters, as De Bary first showed with P. dianthi, through the stomata, or, as Ráthay † points out with P. malvacearum, it enters, like the germ-tube of Tubercinia trientalis, between the epidermal cells, and then pierces laterally into the side of the adjacent cell.

If the germination of the promycelial spores takes place in water, and not upon their proper host-plant, the germtubes sometimes become swollen at their extremities, so as to form reserve spores in the same manner as has been previously described with the uredospores (Plate III. Fig. 24).

The mycelium produced from a promycelial spore in the tissues of its proper host-plant in due time gives rise to a fresh spore-development. This spore-development, however, varies in different cases.

I. In certain species the mycelium produces spores which are exact counterparts of the original teleutospores (Micropuccinia).

2. It may give rise to teleutospores similar in general appearance as to its progenitors, but endowed with the faculty of immediate germination (Leptopuccinia, etc.).

3. It may give rise to a crop of uredospores, which may

* De Bary, "Champ. paras.," Ann. Sc. Nat., 4° sér, tome xx. p. 84 (reprint).

Ráthay, "Ueber d. Eindringen. Puccinia Malvacearum," Verhandl. d. Kk. Zool. bot. Ges., band xxxi. (1881), t. I.

be typical of the species in question.

There are instances,

however, in which, instead of being truly typical, these uredospores depart in some degree from those subsequently found in the life-history of the Uredine. For example, in Triphragmium ulmaria the primary uredospores do not differ in their individual form and size from the secondary, but the former occur in large dusty sori principally on the petioles and midribs of the host-plant, while the latter are much smaller and scattered over the under-surface of the leaves. A more common deviation, however, consists in the association of the primary uredospores with spermogonia (Brachypuccinia).

4. In other instances the mycelium produces spermogonia and æcidiospores. The acidiospores may be upon the same species of host-plant upon which the teleutospores occur (Auteupuccinia), or upon some plant of a totally diverse nature (Heteropuccinia)

The teleutospores of Endophyllum, although they are produced in the same way and closely resemble æcidiospores, yet in germination they behave like the teleutospores of Puccinia (Plate IV. Fig. 7). In Coleosporium (Plate IV. Fig. 9) each cell produces a single promycelial spore, while in Melampsora (Plate IV. Fig. 8) and Chrysomyxa (Plate IV. Fig. 10) three or four are developed from each promycelium, as is also the case with Cronartium.

CHAPTER VII.

HETEROECISM.

History. The fact that a certain number of Uredines possess the faculty of passing a part of their lives upon one plant, and the remainder of it upon another and a totally different one, is so remarkable that until quite recently there were persons who declined point-blank to believe it. It is quite unnecessary now to undertake seriatim to answer the theoretical objections which have been raised against the fact that heterocism does occur, for the simple reason that these objections are only theoretical. The process of simply placing the spores of the fungi in question upon their various host-plants is so easy, that any one wishing to appeal to Nature herself can do so with very little trouble.

The first Uredine in which this peculiarity of development was observed was Puccinia graminis, the wheat mildew. The mildew of wheat has, as a blight, probably been known from remote antiquity. The Romans held a festival on April 25-the Robigalia, or Rubigalia—with the object of protecting their fields from mildew. The sacrifices offered on this occasion consisted of the entrails of a dog and a sheep, accompanied with frankincense and wine.* In Wickliffe's Bible, the suggestion is made that

* Smith, "Smaller Dictionary of Greek and Roman Antiquities," 5th edit. (1863), p. 322.