THE SKELETON OF THE PLANT 



39 



ment of the supporting and conducting tissue at an early 

 stage of its life, and the latter indicates the condition 

 after several months, during which a large formation of 

 secondary vascular tissue has taken place. 



The structure of a coenocyte shows a similar mode of 

 formation of the skeleton to that of 

 a multicellular plant-community. 

 In this case, however, the several 

 protoplasts are not furnished with 

 separating walls. The only skele- 

 ton is the external membrane which 

 limits the whole structure, and 

 which is formed by the conjoint 

 activity of them all. In compound 

 or septated coenocytes we have in 

 addition certain transverse walls 

 crossing the interior and giving a 

 greater degree of strength to the 

 whole body. These separating 

 walls have a similar origin. 



The primary cell-wall which 

 clothes the unicellular plant, and 

 which serves as the original sup- 

 porting membrane of the separate 

 protoplasts of a community or 

 colony, is, when first formed, a 

 clear, transparent, extensible, and 

 elastic membrane, which remains 

 in contact with the protoplasm so 

 long as the latter is living. Blinder 

 certain conditions it is capable of 

 absorbing considerable quantities 

 of water, and in consequence swell- 

 ing to a greater or less extent. 

 Under ordinary conditions it is freely permeable by 

 water. It is usually said to be composed of a sub- 

 stance termed cellulose, whose chemical composition is 



SUSPENSOR, THE TWO SEG- 

 MENTS OF WHICH HAVE A 

 CCENOCYTIC STRUCTURE 

 (After Guignard.) 



The rounded bodies in the seg- 

 ments of the coenocytes are 

 the nuclei of the protoplasts. 



