STELAR THEORIES 



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By the union of the meristeles of the astelic type, a continuous 

 hollow vascular cylinder is reconstituted, which differs from the 

 medullated monostele on account of the presence of an internal 

 endodermis, and is termed gamodesmic. As an example the 

 rhizome of Equisctum sylvaticum may be cited. 



Thus far the theory accounts for the derivation of several 

 distinct types of structure, viz. the medullated monostele, the 

 astelic, and the gamodesmic conditions. 



But there is an alternative line of development ; the primitive 

 monostele may undergo successive branching, so that the 

 polystelic (or dialystelic) condition results, a very common 





rr 9 .i. 



Diagram of a transverse section through the stem of an astelic plant. 



arrangement to be met with in ferns, and which also occurs 

 in certain Angiosperms, e.g. Primula Auricula (fig. '4, c). 



In a transverse section of such a polystelic stem the appear- 

 ance may be exactly like that obtaining in many astelic axes. 



In much the same way as the meristeles unite to form a 

 gamodesmic cylinder, so also may the separate steles of the 

 polystelic phase unite together to form the gamostele, or, as it 

 is frequently termed, the solenostele, e.g. Marsilia and Loxsoma 

 (figs. 2 and 3). 



In testing this theory two lines may be pursued : 



1. Van Tieghem paid practically no attention to the ontogeny 

 or development of the vascular structures. It is clear that the 

 examination of the development of these tissues should show 

 whether the polystele is formed by the successive branching of 



