Evolution of Plants 335 



ation, which reaches its growth climax in the formation of 

 spores, and it shows, up till then, the double number of chro- 

 mosomes at each cell-division. Therefore we speak of the 

 egg-producing and related cells as having a haploid number 

 of chromosomes, the succeeding or spore-producing growth 

 as having a diploid or doubled number. 



As the spores mature, however, they throw off and break 

 do^Ti so much chromatin material that on final maturation 

 they show only half the number of chromosomes. So when 

 each spore has matured and germinated it gives rise to a new 

 sexual generation with haploid chromosomes, that in turn 

 reaches its chmax in the production again of male and female 

 sexual cells, each with a like number. 



In beginning now to trace what we would regard as the 

 probable and approximate steps of advance from the algse up- 

 ward, it is a matter for regret that we still know too little as 

 to the above haploid and diploid cytological details, for the 

 different genera involved. But so far as accurately known 

 thev will be utilized. 



While accepting Coleochcete, with Pringsheim and many 

 successors, as the nearest living representative of those algae 

 that advanced from the Mycoidacese or Pleurococcacese to the 

 degree of bryophytic or moss dignity, there is no need to view 

 Coleochcete other than as a related organism to the main line 

 of bryophytic advance. The nearest living group of higher 

 grade than it seems to be the Ricciacese, a simple division 

 of the Hepaticse. This means however that many intervening 

 types must have become extinct, the approximate structural 

 characters of a few of which we may vaguely attempt to out- 

 line, and so one or two of these are suggested below. 



But in this evolving advance two fundamental features are 

 revealed. First it may be said that all future specialization 

 and modification in plant-forms occurred to a diminishing 

 degree in fresh water, and to an increasing degree on a moist 

 or even fairly tenacious substratum, and ultimately on land. 

 So a great and ever multiplying congeries of marsh and ulti- 

 mately terrestrial genera originated which only in rare cases 

 sent isolated outliers toward or into the seashore. 



