BROWN ALGAE 



389 



sometimes lime-encrusted. In the warmer waters some of these contribute 

 to the formation of Coral reefs, and have been active in this way from early 

 geological times. The chief feature they have in common is their method 

 of sexuality, which may be illustrated in the simple case of Nemalion. The 

 male organs are unicellular, the whole content of each cell escaping as a naked, 

 non-motile spermatium (Fig. 290, 1). The female organ is a carpogonium, 

 consisting of a cell with an enlarged base, and elongated upwards into a fila- 

 mentous trichogyne. This receives the non-motile spermatium, and then 

 shrivels. Carpospores then arise directly or indirectly from the enlarged 



O 



Fig. 290. 



Nemalton multifxdum. 1, Branch bearing antheridia to the left and a carpogonium 

 to the right, with spermatia, some of which adhere to the trichogyne. 2-5 are 

 successive stages of development ot the very simple fruit bearing the carpogonial 

 buds. (After Kny.) 



base. Fertilisation is indirect, in the sense that the nucleus of the spermatium 

 received by the trichogyne is passed down to the base of the carpogonium, 

 where fusion and bud-formation follow (Fig. 290, 4, 5). This is the lead- 

 ing character of the Red Algae, and it is worked out in some of them with 

 extreme complication of detail in the method of transfer of the nucleus. An 

 example of a not infrequent type of fruit-body of Red Seaweeds is shown in 

 Harveyella (Fig. 291), where the carpogonium produces branches (black in 

 the figure), from the ends of which the carpospores are given off. 



In some Red Algae such as Nemalion, which is one of the simplest of them 

 all, no other propagative organs are known. But in most of them tetraspores 

 are found, in the production of which reduction of chromosomes has been 

 demonstrated. The nuclear cycle has been fully worked out in the genus 



