24 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



the time for propagation arrives. In land-plants the cellular structure 

 is general and the several cell-chambers are separated from one another 

 by firm walls. It is no part of our purpose however to describe here 

 the inner structure of plants ; what has been briefly stated is all that is 

 necessary from the organographic point of view. It will be readily 

 understood that there are many intermediate conditions existing between 

 the categories just described ; for example, amongst the Siphonocladiaceae 

 the filiform branched thallus consists of polyergic cells. 



We do not propose to depict here the relationships of configuration of 

 monergic plant-bodies. It has been possible in a large number of cases 

 to discover a relationship between their forms and their life-functions. 

 We see this, for example, amongst diatoms. The monergic cells of fixed 

 species have a different construction from that which obtains in the actively 

 moving or floating species. It is also clear that the pear-like form of 

 most swarm-spores is especially favourable for their movements. In other 

 cases however we know so little regarding the special life-relationships 

 of the plants that we are quite unable to speak with certainty ; we 

 cannot, for example, say whether the rod-like or sickle-like desmids have 

 relationships of a kind different from those of the plate-forms. 



Transitions from monergic to polyergic forms have been found in 

 the most different cycles of affinity. They are brought about by the 

 energids which arise in process of division remaining in union one with 

 the other instead of separating. Naegeli 1 long ago described this as 

 follows : ' The cells which in the simpler plants separate as germs and 

 represent the beginnings of new individuals become in the next higher 

 plants a pertion of the individual organism and prolong the ontogeny in 

 a corresponding degree.' 



The degree in which the single energids are united with one another 

 may be more or less intimate. A polyergic plant is either an energid- 

 colony or coenolimn (cellular or non-cellular) in which a division of labour 

 between the several energids has not yet appeared and each energid is 

 capable of living for itself; or the energids exhibit a division of labour 

 and although in union with one another are therein different from one 

 another they form an energid-dominion. This is what has come to pass 

 in the majority of the polyergic plants. There are of course many transi- 

 tions between these two conditions, and their separation is in a measure 

 artificial, being based upon extreme relationships. 



1 Naegeli, Systematische Ubersicht der Erscheinungen im Pflanzenreich, Freiburg i. 13., 1853; 

 Id., Mechanisch-physiol. Theorie der Abstammungslehre, p. 332. 



