94 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



It is to be remembered also that, as was observed by the early 

 students of the group, each cell starts its development as a rounded 

 or slightly ovoid ciliated swarmspore and that the organization 

 of the colony is achieved by the cells while they have this form. 

 So far as their surface tension relations are concerned they behave 

 as mere viscid droplets of jelly-like material, both in the form 

 which they assume and the form relations into which they enter 

 with each other. The colony as it first appears in the vesicle 

 from the mother cell is a plate of rounded or ovoid bodies. The 

 more or less lobed form of the cells is wholly a result of their 

 growth; though it appears immediately on the cessation of the 

 swarming movement or even before movement has entirely ceased, 

 so that very young colonies are quite exact miniatures of the 

 mature ones. 



The swarmspores are practically globular or oval plastic bodies 

 and the problem of their combination to form a flat plate in which 

 they shall have the characteristic arrangement found in the adult 

 colony is essentially that of combining sixteen such units into a 



Ik r< A 



Fig. la. Pediastrum Boryamim, sixtccn-ccUcd colony, X about 600. The original 

 enlarged about one half in reproduction. 



b. Diagram showing the cell relations in such a colony. Dimensions obtained by 

 averaging the corresponding sides and angles right and left of the a.\is m-n, except in 

 case of the angles marked by an asterisk in the table, page 98. The dimensions of 

 the cells in the diagram were measured on a photograpliic enlargement about twice the 

 diameter of figure a. The diagram has been reduced about one fourth in reproduction. 



