264 



Siphonocladiales 



general the formation of the spores is basipetal, the first- formed being at the 

 tips of the branches. Twin-spores frequently arise from one mother-segment 

 and even three in a row may be successively formed. In some instances 

 spores are formed at the lower end instead of at the upper end of a segment. 

 The spore germinates in opposite directions from the two poles and is very 





Fig. 169. 



Pithophora Cleveana Wittr. A, part of thallus with resting-spores, x 4 ; B, terminal 

 spore; C, intercalary spore ; D, paired intercalary spores. B D, x 105. 



early divided by a transverse wall, one half giving origin to the cauloid 

 portion of the thallus and the other to the rhizoidal part. The latter consists 

 generally of one segment and is rarely ramified. 



Pithophora-plants are also able to propagate themselves in another manner 

 by means of 'prolific cells' which are of the nature of hypnocysts. The 

 latter arise from ordinary segments, usually of the main axis, without any 



