148 HISTORY OF BOTANY 



nuclei of the cells of the sporophyte. In 1894 Strasburger 

 expressed the view that this difference in the number 

 of the chromosomes was universal between the game- 

 tophyta and sporophyta of all Archegoniatae, so that 

 if the number in the former phase be represented by 

 x then the number in the latter is 2%. A reduction 

 at some stage in the life cycle from 2% to x was thus 

 essential, and Strasburger fixed this halving at the 

 point where the spore mother cell gave rise to the 

 carpospores. Incidentally it may be noted that this 

 reduction division may take place somewhere else, e.g. 

 before the formation of ovum and sperm, as in the case 

 of Fucus, where no asexual reproduction nor carpospores 

 occur. Of course, if this cytological distinction could 

 be shown to be universal and fundamental and not 

 merely physiological and adaptive, it would give us a 

 criterion by which the homologies between the two 

 types of .life cycle might be settled. 



The antagonism between the two schools was accentu- 

 ated by Lang in 1909 when he put forward what he 

 termed an " ontogenetic theory of alternation." " In 

 organisms without any alternation of generations," 

 he says, " there is only one type of body, and any germ 

 cell, whether sexually or asexually produced, can be 

 regarded as a specific cell with the power of giving rise 

 under the proper conditions to a new individual like 

 the parent/' In cases where a definite alternation of 

 generations occurs " we meet twice in the life cycle with 

 a germ cell, i.e. a cell capable of developing into a new 

 organism. These two germ cells are the spore and the 

 fertilised egg. The result of the development of these 

 two cells may be closely similar or widely different/' 

 As illustrations of the case where the two germ cells 

 produce morphologically identical vegetative bodies he 

 gives Dictyota and Polysiphonia, while the Bryophyta 

 and Vascular Cryptogams present us with two very 

 dissimilar generations, the one derived from the spore, 



