COLONIES OR COENOBIA IN THALLOPHYTA 



I. COLONIES OR COENOBIA. 



The outer form of the colonies is very variable. I shall here only 

 cite a few examples in order to explain what we mean by them. 



A. COLONIES WHICH ARE NOT FIXED. 



I. COLONIES OF NAKED ENERG1DS, OR, NON-CELLULAR ENERGID-COLONIES. 



We find these in the plasmodia of the Myxomycetes (Fig. 2). The advantage 

 which the plant obtains by 

 the possession of the colonial 

 form is manifestwhen spore- 

 formation takes place, and 

 especially in spore-distri- 

 bution. An energid-colony 

 can construct larger fructi- 

 fications which are better 

 adapted for the distribution 

 of the spores. It is espe- 

 cially instructive to note 

 that in the Acrasieae, one 

 of the lowest groups of this 

 developmenta series, the 

 vegetative energids remain 

 single ; they form no plas- 

 modium and only with the 

 approach of spore-formation 

 do they creep together. In 

 Guttulina, a member of the 

 group, no fructification is 

 even formed, and the only 

 advantage we can suppose 

 the plant derives from the 

 creeping together of the 

 energids, or of the heaping 

 together of the spores, is 

 that such spore-heaps offer 

 a more favourable condition 

 for the distribution of the 

 spores than would be the 

 case were the spores to remain isolated. If now, without further considering 

 the utilitarian question, we assume that the originally free energids, which here 

 may be termed amoebae, exercise an attraction, which is probably a chemotactic 

 one, upon each other, we find that, starting from the Acrasieae, the Myxomy- 

 cetes exhibit a progressive series in which the formation of spores is postponed to 

 a period gradually getting later after the formation of the colonies, so that between 



FlG. 2. Chondrioderma difforma, one of the Myxomycetes. Germina- 

 tion and formation of plasmodium. a- A spores and the naked flagellate 

 energids which swarm out from them ; /', k, the energids have become 

 amoebae ; / amoebae creeping together to form an energid-colony ; 

 in, n, older energid-colonies, the plasmodium ; a-m magnified about 540; 

 magnified about 90. Lehrb. 



