56 PLANT LIFE 



cellular colonies. This proves at once that 

 each is suited for existence, in so far as physical 

 conditions are concerned. We may indeed 

 inquire whether the more specialised colonies 

 actually do succeed better at all than their 

 simpler unicellular relatives. In the higher 

 forms there is the accumulation of food- 

 supplies, and such consequent advantages 

 as accrue from the possession of these re- 

 serves, but it is clearly impossible to see how 

 this could account for the origin of the multi- 

 cellular types. Perhaps, indeed, we are 

 attacking the problem at the wrong end by 

 regarding it as one of profit and loss at all. 

 It seems at least as likely that the same sort 

 of influence which we discern to subsist 

 between, and to determine the organisation 

 of the units of a specialised colony, operates 

 in a similar, albeit in a simpler and cruder, way 

 between the potentially free omits of a primi- 

 tive colony. In other words, the cause of 

 coherence is primarily independent of ad- 

 vantage or disadvantage, and may hardly 

 exceed an almost accidental lack of disunion 

 (e.g. in Spirogyra); or it may depend upon 

 some attractive influence which causes the 

 units, primarily separate, to cohere in clusters, 

 as happens in the series of algae exemplified 

 by well-known forms such as Volvox or 

 Hydrodictyon. 



