428 HARPER— ORGANIZATION, REPRODUCTION 



and is a metidentical character in Detto's sense. The color as such 

 may be thought of, at least, as present throughout the whole process 

 of producing the daughter cells from the mother cell. The cylin- 

 drical form of a cell of Spirogyra may also be inherited directly as 

 such in this same fashion by the division of a cylindrical mother cell 

 into two shorter cylindrical daughter cells. 



In the case of the cell of Pediastrum the lobed or spinous form 

 disappears in the successive bipartitions of the mother cell and we 

 have an oval ciliated swarmspore essentially similar in form to 

 those of other more or less distantly related green algse. Repro- 

 duction by cell division here has involved the return to what is 

 generally assumed to be a more primitive type of cell both as to its 

 form and its motility. The adult form typical of the species only 

 reappears as a result of ontogenetic development by which the 

 primitive cell form becomes differentiated into the more specialized 

 adult. In all filamentous and coenobic algse which reproduce by 

 swarmspores we have this advance beyond the conditions in Spiro- 

 gyra, and related types in which the germ cell dift'ers only in size 

 from the adult. The reproductive cycle in Pediastnmi, for example, 

 parallels that of the higher plants in its essential stages. A mother 

 cell forms undifferentiated germ cells which become specialized dur- 

 ing ontogeny in their form and structure and by their combination 

 produce the many-celled colony which shows also a more or less 

 highly specialized and adaptive organization. In the higher meta- 

 phytes it is not so directly obvious as in Pediastrum that the form 

 characteristics of the many-celled plant body are the direct expres- 

 sion of the form, polarities, adhesiveness, and other characteristics 

 of the individual cells. The inheritance of cell form and of the 

 form of the colony are indirect as compared with cell color. To be 

 sure, in the latter case swarmspores may be relatively or entirely 

 free from the green color which then reappears in ontogeny but the 

 transfer of the capacity to form green pigment is assumed to involve 

 the division of plastids which thus carry on the pigment-forming 

 bases, chromogens, just as the nucleus, chromosomes, etc., are per- 

 petuated directly by division. In the vegetative reproduction of 

 these simple algae we do not need to say that the capacity to form 

 chlorophyll is represented by an hereditary factor in the germ plasm, 



