ULOTRICHALES 



55 



are formed without any nuclear divisions being involved. In 

 Sphaeroplea annulina the ova are non-motile but in S. cambrica 

 they are biflagellate, and so it may be argued that the motionless egg 

 has been evolved from the motile one by loss of flagellae. In the 

 antheridia, on the other hand, the nuclei undergo division and 



Fig. 41. Sphaeroplea. A, S. annulina, portion of thallus. B, S. annulina, 

 chloroplast. C, structure of septum in 5. Africana ( x 375). D, female plant with 

 ova and antherozoids. E, male plant. F, young zygote. G, zygote with thickened 

 wall. H, I, young gametophytes. J, spores emerging from zygote. K, L, 

 S. Africana, transverse sections across the septa ( x 375). (A-C, K, L, after 

 Fritsch; D-J, after Oltmanns.) 



numerous elongated narrow antherozoids are formed which are 

 liberated through small holes, subsequently penetrating the oogonia 

 through similar perforations. The fertilized ovum (oospore) becomes 

 surrounded by a hyaline membrane, and then inside this two new 

 membranes are laid down, after which the first one disappears. The 

 new external membrane is ornamented and the contents of the 

 oospore are now a brick red. Germination stages are only known 



