THE ALGAE 



157 



elongated, starch-filled elements which are destined to play later an important 

 part in the formation of the reproductive cells. The assimilatory zone then 

 begins to form procarp branches. Each procarp consists of four cells. 

 The lowest cell is termed the basal cell and is in protoplasmic connection 

 with the collecting cells of the thallus. It is followed by two intermediate 

 cells, and the branch is terminated by the carpogonium, which is more or 

 less flask-shaped, with an enlarged basal part containing the female nucleus 

 and an elongated trichogyne which projects beyond the outer limit of the 

 assimilatory zone into the water. The spermatium becomes united to the 

 trichogyne^ and the male nucleus passes down the trichogyne and presumably 

 fuses with the female nucleus. 



SPERMATIA 



COLLECTING 

 CELL 



Fig. 144. — Chondrus crispus. A, Abstriction of 

 spermatia at surface of thallus. B, Procarp 

 branch with trichogyne emerging from sur- BASAL CELL 

 face of thallus. {After Darbishire.) 



After fertilization a wall is laid down cutting off the trichogyne which 

 then withers and disappears. The carpogonium now unites with the basal 

 cell which thus functions as the auxiliary cell, and the zygote nucleus passes 

 into it. 



From the auxiliary cell a number of filaments now begin to develop. 

 These are termed the gonimoblast filaments and are characteristic of many 

 Rhodophyceae. They form secondary connections with the neighbouring 

 collecting and conducting cells from whose reserves of starch they draw 

 nourishment. From the tips of the gonimoblast filaments two or three cells 

 are cut off, each of which produces one carpospore. These spores are 

 liberated into a cavity (Fig. 145), formed by the collapse of the exhausted 

 cells of the conducting and central filaments, which may be regarded as a 

 cystocarp, a term used for any structure enclosing carpospores. 



The mature carpospores are roundish bodies which are at first devoid 

 of a cell wall. They possess a very dense cytoplasm with a large amount 



