THE ALG^E 



129 



cilia. In the Kelps the sporangia are formed in dense masses (Fig. 

 99, A), either on the ordinary leaves, or upon special sporophylls. 

 The sporangia are formed singly at the base of club-shaped hairs, or 

 paraphyses. These are the only reproductive bodies known in the 

 Laminariaceae. 



In many of the Phaeosporeae, however, there are formed the 

 plurilocular sporangia, or, perhaps more correctly, gametangia, as it 

 seems probable that the cells developed from these are gametes. In 

 Ectocai'pus the young gametangium is a short lateral branch, divided 

 transversely into several cells (Fig. 95, C, D). In these, series of 

 longitudinal and transverse walls arise, resulting in a large number 

 of nearly cubical cells, each of which gives rise to a biciliate cell, 

 much like the non-sexual zoospores, but probably always incapable 

 of developing further without fertilization, although this has only 

 been demonstrated in a small number of forms. 



The resulting zygote germinates at once, as do the zoospores. 



Germination. So far as the development of these forms has been 

 followed, the germinating spore develops first a cell-row, which, in 

 the larger forms, like the Kelps, soon produces a flat thallus. This 

 gradually assumes the characters of the 

 mature plant. Nereocystis (Fig. 98, A) 

 will illustrate the more important points. 

 The young plant shows the stem, with the 

 branching root, and above it the expanded 

 lamina. The point of most active growth 

 is at the junction of the stem and lamina. 

 Here, by active growth, the first indication 

 of the float is formed, and growth is very 

 active at the base of the lamina, which 

 soon splits along the middle line into two 

 equal parts. These divide repeatedly in 

 the same way, so that two bunches of 

 leaves are finally produced. 



In some of the perennial forms, like 

 Laminaria, which renews the lamina each 

 year, and Lessonia, the stem increases 

 annually in thickness, and a section shows 

 a series of rings curiously like those in 

 the woody stems of the higher plants. 



The Cutleriaceae 



Intermediate in some respects between 



the typical Phseosporeaa and Fucaceas is 



J . 



a small family, the (Jutleriaceae. The 



- 100. Cutleria multijida : 



a ' femal s rus; b ' . a l e 

 sorus, highly magnified. 



(After MURRAY.) 



