XIV. 



NOTES ON THE SORI OF MACROCYSTIS 



AND POSTELSIA. 



THE occurrence and function of conceptacular bodies in so many 

 genera of olive-brown Algse is a subject that has received much 

 attention from phycologists. Without entering on a discussion of the 

 origin of these structures, it has seemed to us that the peculiar position 

 of the sori in the two genera, Macrocystis and Postelsia, throws 

 additional light on the function of conceptacles ; we have found the 

 sori in these plants confined to the furrows of the sporophyllous leaves, 

 a position of shelter such as is afforded elsewhere by conceptacles. 



The Laminariacecs have been subdivided by Mr. Setchell into three 

 groups, of which the types are Laminaria, Lessonia, and Alaria, and 

 in that of Lessonia he has placed Postelsia and the gigantic Macrocystis, 

 The members of the Lessonia group are characterised by the complexity 

 of their fronds, due, in the case of Macrocystis, to unequal splitting 

 of the growing tissue, so that, while the main growth of the thallus 

 continues at the apex, and becomes a stem-like member, the parts that are 

 split off develop into long narrow leaves with large air-bladders at the 

 base. When quite young the fronds are thin and smooth, the older 

 members become thicker and stronger, and are longitudinally wrinkled 

 or furrowed. Along the margin spines occur, which develop after the 

 splitting has taken place. 



Rosenthal published in Flora, 1890, a detailed account of the anatomy 

 and development of the vegetative organs of Macrocystis luxurians (== M. 

 pyrifera.} The leaves have an epidermis of one or sometimes two cells 

 in depth. These are small, compact, and full of contents. Within 

 this layer are the cortical cells, which become larger towards the centre 

 of the frond, and, finally, the central tissue, which in the older leaves 



84 



