AND INHERITANCE IN PEDIASTRUM. 427 



The prevailing oblong, four-lobed form of the Pcdiastrmn cell 

 is probably adaptive for the general metabolism of the cells and is 

 also the form which permits the closest possible approximation to a 

 least-surface configuration in a colony composed of units arising by 

 binary fission. It is the form of cell which would be expected to 

 arise imder the pressure relations existing in such plates of cells 

 held together by adhesion and yet as noted it can and does arise in 

 cells almost entirely free from such contact and pressure relations. 

 We have here evidence that a cell form which may well have arisen 

 first simply as a response to environmental stimuli has become fixed 

 in heredity until now the series of growth processes by which it 

 develops can go on quite independently of the stimulative conditions 

 which originally called them forth. In Pcdiastnim we do not have 

 the extreme difiterentiation of germ plasm and soma which under 

 the conditions in the higher metaphytes makes such direct interrela- 

 tions of environment and heredity so difficult to conceive. 



It is sufficiently obvious that the oblong four-lobed form is 

 directly transmitted through vegetative reproduction by cell division 

 and there is no reason to question that the same is true in sexual 

 reproduction by the fusion of gametes. In asexual reproduction 

 the mother cell divides by successive bipartitions to produce a swarm 

 of oval ciliated swarmspores which at first show no trace of their 

 adult form. I have noted, however, how promptly, almost instan- 

 taneously, the four-lobed form appears as the swarmers come to rest 

 in the contact and pressure relations of the colony and with the very 

 first growth expansion, so that almost as soon as it is formed the 

 young colony has all the essential structural characteristics of the 

 adult. 



We may consider briefly at this point the difficult question as to 

 the method of representation and transmission in heredity of the 

 characters of differentiated tissue cells and the characters of tissues, 

 organs and entire organisms considered as wholes. 



Inheritance of Cell Form. — The inheritance of cell form cannot 

 be said to be direct in the sense that the inheritance of green color 

 may be direct. The division of a green cell givis at once two green 

 cells. Greenness is inherited as such by division of the chloroplast 



