THALLOPH y TA— ALG^ 



51 



^-■a 



lopment of the structure varies very greatlj' iia different groups, 

 leading in all-ultimately to the production of a fruit-like structure 

 which is known as a cystocarp, and which is really the sporophyte 

 phase of the plant. It consists essentially of a cluster of car- 

 posporangia, variously arranged and often enclosed in a definite 

 encasement of filaments or cells. There are five different types 

 of formation. The first is seen in the NEMALiONACEa; ; here 

 from the fertilised carpogonium filaments known a.sgonimoblasts 

 grow out, often in dense clusters. The terminal cells of the 

 filaments are the carposporangia, and each produces internally 

 a single carpospore. The whole group constitutes the cystocarp 

 (fig. 800), which is consequently not enclosed in any specially 

 differentiated case. Some- 

 times the gonimoblasts arise '*'■ 

 from the upper part of the 

 carpogonium, sometimes 

 from its side. In some of the 

 famiHes the cystocarp is im- 

 mersed in the tissue of the 

 thaUus. In the Gelidese the 

 ceils of the gonimoblast be- 

 come united here and there 

 to certain cells of the thallus, 

 from which it absorbs nou- 

 rishment. 



The second type is fur- 

 nished by the GigaetinacejE ; 

 in this, besides the branches 

 which carry the carpogonia, 

 other special cells are pro- 

 duced on the thallus near 

 them, generally in pairs. These cells are known as auxiliary 

 cells. When the carpogonium has been fertilised it does not give 

 rise at once to gonimoblasts, but puts out a short protuberance 

 known as an ooUastema filament. This makes its way to an 

 auxiliary cell, and the contents of the two fuse. The gonimo- 

 blasts arise from the resulting cell and branch in the interior 

 of the thaUus, the cystocarp being thus embedded in its sub- 

 stance. The fruit thus arises from the auxihary cell rather than 

 immediately from the carpogonium as in the NemalionaceEE. 



The third type, characteristic of the Rhodomeniace^, is still 

 more complex. The formation of the cystocarp is indirect as in 

 the last case, the carpogonimri conjugating with an auxiliary cell. 



Fig. 8U0. 1. Cystocarp of Nemalion. 

 a. Carposportfs. 



2. Cystocarp of Lcjolisia. 6. Carpo- 

 spores. c. Wal' of cystocarp. d. Carpo- 

 spore escaping. After Kuy. 



