Evolution of Plants 337 



to an aquatic life, while that known as the asexual or sporo- 

 phytic (characterized by a full or diploid number of chro- 

 mosomes) generation as clearly suggests advancing adaptation 

 to a land life. 



In returning now to a study of the relationship between 

 the green algse and the Ricciacese, we would accept it that, 

 while Coleochcete indicates valuable transition characters, large 

 groups of connecting genera, that would have enabled closer 

 connection to be traced, are now extinct. 



In all of these the germinating spore probably formed first 

 a swarmspore tube of passive character (p. 340), that became 

 in the higher examples the "protonema." This in turn gave 

 rise, by repeated divisions, to a somewhat flattened thallus, 

 that either grew radially into a condensed dorsi ventral mass, 

 or by elongation produced a thread-shaped body that length- 

 ened dorsi ventrally. In all of them simple cellular down- 

 growths from the mass became attacliing organs or rhizoids, 

 while apex cells by continued division produced dichotomous 

 or false dichotomous branches. Each vegetative cell thus 

 produced retained a single chromatophore \\'ith pyrenoid center 

 in Coleochcete, and this is retained in the Anthocerotese group 

 of the Hepaticse, that for many reasons should be regarded 

 as an early derivative from protohepatic organisms, and that 

 evolved separately from the Riccieae. But in the last the 

 originally single chromatophore of each cell divided — as already 

 shown to have happened in higher green algae — into several 

 separate masses. 



The sexual plant body in Coleochcete is usually of one layer, 

 but a tendency toward two layers is seen in types hke C. scidata. 

 But in Thallocarpiis and SphcerocarpuSy both simple genera 

 of Hepaticse, the thallus consists of a single cell layer, except 

 along the middle line, where it is subdivided into several zones. 

 Extinct forms, in which two to many cell layers developed, 

 must have connected both of the above with the Riccieie, whose 

 thallus now consists of six to ten similar or more often dis- 

 similar zones, the lower being made up usually of closely united 

 pale cells, from which attacliing rliizoids and cellular scales 

 arise, while the upper is generally spongy, and contains abun- 

 dant chloroplasts in the cells. 



In all of them outgrowths from the upper surface of the 

 thallus appear as fine delicate hairs, that are probably sensory 

 in function. 



