M. Arbaumont found that young seeds gave rise to plants of extraordinary vegetative vigour; moderately aged ones gave rise to corresponding moderately vigorous plants with both male and female flowers; while older seeds gave rise to still less vigorous plants, but which, when properly nourished, formed female buds.* M. F. Cazzuolat also found that melons raised from fresh seed bore a larger proportion of male flowers than female; while older seed bore more female flowers and this has been confirmed.

Another interesting result was obtained by M. Triewald, who grew twenty-one out of twenty-four melon seeds which were forty-one years old. The branches were very narrow, yet they produced early and plenty of good melons.‡ Α cause of the differences of vigour in the plants raised from seeds of different age is, perhaps, connected with the fact that fresh melon seeds contain a neutral oil, which becomes more and more acid by keeping. This increased acidity coincides with a diminished germinative power; § and proportionately, therefore, less liable to run into excessive vegetative growth.

The next condition to be observed is that resulting from sowing seeds of diclinous plants thickly or thinly. Hoffman's experiments || in this direction showed that 283 male

*Bull. de la Soc. de Bot. de Fr., 1878, p. 111.

Bull. de Tuscan. Hort. Soc., 1877.

Gard. Chron., 1879, p. 470.

§ M. Ladureau in Ann. Agronomiques. Mr. Darwin also found that fresh seeds of Iberis grew at first more vigorously than others (Cross and Self-fertilisation, etc., p. 103).

Gard. Chron., 1879, p. 762; see also Bot. Zeit., xliii., 1885, p. 145, seqq.; also Jenaisch Zeitschr. f. Naturwiss, xix. (1885), sup. ii., pp. 108112. The following were the plants with which he experimented: Lychnis diurna, L. vespertina, Valeriana dioica, Mercurialis annua, Rumex Acetosella, Spinacia oleracea, and Cannabis sativa.

plants appeared, and 700 female, in the thickly sown plot, while only 76 males occurred when thinly sown. This has been paralleled in America, where Mr. Meehan, of Philadelphia, has noticed how Ambrosia artemisiafolia, if growing vigorously, has a proportion of female flowers largely in excess of the males; but in fields where the grain has been cut, and this "Rag-weed comes up in thick masses late in the season, the individual plants nearly starving each other, male flowers are very numerous, and some are wholly male. Prantl also observed that the crowded prothallia of Ferns gave rise to more antheridia, and scattered ones more pistillidia. Pfeffer, too, noticed the same fact with Equisetum.

In these cases we seem to have results exactly the reverse of those of the melon seeds: but while in the latter the male flowers were accompanied by the precocious and excessive vegetative energy, the female were prevented from appearing at all; for it must be remembered that normally male flowers of melons appear before the females. In the case of thin sowing, the plants were in a natural and healthy condition: but when crowded they were starved, and the vital energy, being just enough to develop male flowers, proved insufficient for the female; and, conversely, when thinly sown, "vitality" was not checked, and females were abundant.

The question arises, are all seeds potentially bisexual, and one sex rather than another determined either by an inherent vigorous constitution or by the conditions of the environment during germination and growth? or is there, so to say, a determination of sex, or at least a predisposition, at an earlier stage still? Dr. Hoffman, judging from his experiments, is inclined to the opinion that sex does not reside in the seed, but depends on conditions of germination. Mr. W. G. Smith arrived at the same conclusion, for he says

in his Remarks on some Diacious Plants,* "I think seeds themselves are probably not either male or female, but that after influences produce the sex; as in animals the sex is not developed in the early embryo life of the creature, nor till the embryo has attained a certain age."

On the other hand, F. Heyer thought sex was determined at an earlier period than the ripening of the seed.† Some differences which have been noticed in seedlings of Nutmegs seem to countenance this idea; thus Mr. Prestoe, in his report on the Trinidad garden,‡ says that "the leaf of the female seedling is most perfectly elliptical, with straighter primary veins. In the male plant it is broader towards the point than at the middle, i.e. obovate, and furnished with a point much longer than that of the female. The veins are also curved in towards the point much more roundly than in the latter."

An interesting experiment by Mr. I. Anderson-Henry, recorded in the Gardener's Chronicle of 1876, may be quoted. He says, "I raised a seedling Begonia having female flowers only. It resulted from an experiment I made on the seedbearer by cutting off two of the three lobes which compose the stigma, and fertilising the remaining lobe. I repeated this experiment; and all of the progeny which have yet bloomed, consisting of four or five plants, have likewise all come with female flowers only." This seems to show that the female seedlings were due to concentration of energy to a limited number of seeds. On the other hand, a hybrid Begonia, "Adonis," raised by Mr. Veitch from a summerflowering tuberous variety, "John Heal," crossed with a winter flowering variety (itself obtained from B. Socotrina crossed by a dwarf-flowering tuberous variety), bore nothing

* Journ. of Bot., 1864, p. 232 (note). † Journ. Micr. Soc., 1884, 251. Gard. Chron., 1884, p. 315.

but male flowers-presumably in consequence of some weakness of constitution due to hybridisation.

It would be quite foreign to my purpose to trace the origin of sexes throughout the vegetable kingdom, as I am solely concerned with that of flowers. But what appears to be pretty certain is that the absorption of the pollen-nucleus by the "egg-cell" involves a special form of nutrition, coupled with certain excitant effects. Union between nuclei occurs elsewhere; and as illustrative analogies, one recalls the fact of fusion being normal in the Conjugate, and among zoospores, where no sexual differentiations are observable. Again, in the embryo-sac there occurs the union of two nuclei, one from each tetrad, their function being then apparently to form endosperm. As another case, Mr. Gilburt has described the union of the nuclei of cells constituting a "cell-group," which forms a wood-fibre after the absorption of the septa.*

Of course one of the most essential properties of the pollen-nucleus is to transmit to the offspring characteristics of the male parent: but even this is paralleled in the vegetative system; for an engrafted scion can transfer its peculiarities to the stock, as has occurred with Cytisus Adami, variegated Abutilons, etc.

If, however, we ask what are the actual differences which exist between the male and female energies, and how they have arisen, we at once find that we are completely baffled, and that all speculations are at present futile.

* Morph. of Veg. Tiss., Journ. Roy. Micr. Soc., 1879, p. 806 (note). Schacht observed a similar origin of liber-fibres in the Papaw, each of which was originally composed of three or four cells, but the septa become absorbed; their original positions being only indicated by clusters of pores on the walls (Les Laticif. du Carica Papaya, Ann. des Sci. Nat., 4 sér., viii., pl. 8, figs. 9, 10). Treub, on the other hand, discovered the laticiferous vessels and liber-fibres of the Nettle, etc., to have arisen by repeated division of the nucleus, the partitions not having been formed at all (Arch. Neerl. des Sci. Exac. et Nat., tom. xv., 1880, p. 39).

CHAPTER XXVI.

DEGENERACY OF FLOWERS.

*

INCONSPICUOUS AND CLEISTOGAMOUS FLOWERS.-Degeneracy in plants is as of frequent occurrence as in animals; and just as it implies no pathological or anything of a constitutionally injurious character in them, so, it must be distinctly borne in mind, does it imply nothing of the sort in plants. The word means "down from the genus; like "degradation," it is only a "step downwards." step downwards." It implies retrogressive or at least arrested conditions; but a degraded flower often acquires new features, qualifying it for securing self-fertilisation with a far greater certainty than was the case with its more conspicuously flowering ancestors.

There are several causes which can bring about degradations in the various organs of plants, such as growth in water, subterranean habits, parasitic and saprophytic states, freedom from strains, compensation, etc. Though it would be interesting to trace out the cause and effect in each case, I must content myself with flowers, and particularly the essential organs.

There are two principal causes which may be styled the rationale of degradation in flowers. The first is compensation, when the vegetative system is in too great activity to

*Cleistogamous, "a closed union," i.e. when flowers are selffertilising without opening.