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 junits 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 algz exemplified 
by well-known forms such as Volvox or 
Hydrodictyon. 
