THE DEVELOPMENT OF ORGANISMS 785 



amphimixis. So that the sequence became: Sporophyte-Spore- 

 Gametophyte-Fertilised Ovum-Sporophyte. The sporophyte, with 

 its more vegetative body and its double supply of chromatin, 

 represents the relatively more anabolic preponderance, and its 

 spore-formation had the advantage of securing dispersal. The 

 gametophyte, given over to reproduction to a proportionately greater 

 degree, with a weak vegetative grip in most cases, sometimes unable 

 to survive without a symbiotic fungus (!), and with half the supply 

 of chromatin per cell, represents a relatively more katabolic pre- 

 dominance. Yet in the amphimixis there are the advantages which 

 have been referred to in the section on Reproduction. Thus the 

 pooling of two inheritances, often from separate gametophytes, 

 may promote variability at one time and average off undesirable 

 idiosyncrasies at another. 



In comparing alternation of generations in plants with what occurs 

 in many animals, it should be noticed that in the latter the 

 contrast is often between asexual and sexual phases, or between 

 parthenogenetic and spermic development; that there are no 

 spores in multicellular animals except in a few cases like Trema- 

 todes ; and that the reduction division occurs in the maturation of 

 the egg-cells and sperm-cells. 



In a well worked-out theory, Prof. F. O. Bower has associated the 

 later differentiation of plant metagenesis with the colonisation of 

 the dry land. It must be thought of as beginning in water, for it is 

 shown by many Algce, and the character of the sperm-cell in Crypto- 

 gams implies free-swimming. But the increasing divergence of 

 sporophyte and gametophyte may be associated with the establish- 

 ment of the terrestrial habit. Thus one important feature involved 

 in this change would be the retention of the fertilised egg-cell within 

 the parent-plant — in the archegonium in fact. Since the gameto- 

 phyte was never at home, so to speak, on dry land, unless in such 

 cases as the moisture-loving liverworts and mosses, there was a 

 tendency to lay more and more emphasis on the more vegetative 

 sporophyte, which gradually became the ascendant terrestrial 

 phase. Finally, yet gradually, what corresponds to the prothallus 

 was retained within the shelter of the sporophyte, as in all seed- 

 plants. The general idea is attractive that the ascendancy of the 

 sporophyte and the dwindling of the gametophyte to a vestige was 

 historically associated with the establishment and advance of a 

 land-flora. 



THE FLOWER IN HISTORICAL RETROSPECT.— It is one of 



the strangest paradoxes of the history of science that neither Linnaeus 

 as the father of modern botany, nor even Robert Brown and De 

 CandoUe, though establishing the natural system, had ever imagined 

 the real nature of the flower, any more than has the simple field 



VOL. II E 



