ALGAE AND BRYOPHYTA 659 



of germs. But at least the existence of post-sexual divisions in certain 

 Algae associated more or less definitely with reduction show that the initial 

 structure postulated by our theory does actually exist. At the same time, 

 the Thallophytes present no facts which directly disprove the hypothesis 

 for land-growing plants : they do illustrate, however, other types of cytologi- 

 cally distinct generations, both algal and fungal, analogous, no doubt, to 

 that seen in the Archegoniatae, but probably produced along phyletic lines 

 which were distinct, and subject to quite different external conditions 

 during their development. 



A general objection to the whole theory of antithetic alternation was 

 raised some years ago on the ground of the assumed improbability that 

 new parts should appear in the life history. 1 It was pointed out that 

 nature is conservative, and it was stated that when a new organ is formed 

 it is almost always fashioned out of some pre-existing organ. The adage 

 was quoted " e.v nihilo nilril fit" : the same objection to the whole anti- 

 thetic position has recently been reiterated from the Continent. The reply 

 to this general objection is a very simple one : it is, that the zygote from 

 which our hypothesis starts is not " nothing " : it is a cell, with all the 

 powers and possibilities of a complete and in point of fact a diploid 

 cell. It has already been concluded generally as regards the sporophyte 

 (p. 100) that a living cell which is capable of growth has not a specific 

 and unalterable function : this we may conceive to have been the initial 

 condition of the zygote and of its early products. The hypothesis involves 

 a development of the potentialities of a living cell : the zygote is actually 

 seen in each normal ontogenetic cycle to give rise by gradual steps of 

 development to the whole sporophyte : the theory contemplates a cognate 

 development as having proceeded gradually in the course of descent. In 

 face of the ontogenetic facts the initial objection does not appear to be valid. 



Passing to the more special question of the origin of members, it is 

 necessary to examine the inherent improbability which is assumed to 

 surround their appearance as new structures. It is plain that the difficulty 

 lies in their phyletic not in their ontogenetic origin : for it is a fact which 

 anyone may observe that in the individual development new parts do 

 appear where previously there were none : new axes, new leaves, hairs, 

 emergences, roots, all are originated in this way, each growing out from a 

 spot previously in the individual unoccupied. The position, then, of those 

 who entertain this objection appears to be that what is the rule in the 

 development of the individual is inherently improbable in the evolution of 

 the race. This is surely a new principle in morphology. The practice 

 of the science has been hitherto to hold the exact converse ; the onus 

 probandi lies with those who declare that the origin of organs in the 



1 Dr. Scott. Presidential Address to Section K (British Association /\V/V/V, 1896, 

 996). The position there taken up was substantially that ol Pringsheim (Gtsammclle 

 A hhand. ii. p. 370). It was criticised in my address to Section K (British Association 

 Report, 1898, p. 1032). 



