56 Structure of Hydroclathrus. 







stomata and paraphyses are sunk in slight depressions, whereas in the 

 plants collected at Madras the surface is uniformly even. 



Hydrodathms cancdlatus. H. cancellatus, in outward appearance, 

 offers an entire contrast to H. sinuosits ; the thallus consists of branches 

 which anastomose to form a network with large or small intervening 

 meshes. The whole plant is usually more or less spherical or ovate, and it 

 is found sometimes growing together with and adhering to //. sinuosus or 

 by itself, and attached to some other Alga. 



While one region of the thallus is fully formed and capable of producing 

 sporangia, another may be still in a state of growth. Some of the branches 

 are flattened, others are almost cylindrical. Along the inner side of the 

 latter, i.e., the side which is towards the interior of the whole net, the 

 continuity of the epidermal layer is destroyed, and the underlying tissue 

 appears to be ruptured almost as far as the central line of the branch 

 (plate XV., fig. 3) ; the epidermal layers on either side of the line of 

 division bend towards each other, and a section of such a branch is 

 reniform rather than cylindrical. On all the branches cryptostomata and 

 sporangia are present in various stages of development. Their growth, 

 as far as I have been able to observe it, follows closely that of H. sinnosns, 

 the material to which I had access being too young to show whether 

 vegetative growth takes place from the basal cell of the sporangia, giving 

 rise to paraphyses. 



The point of interest about these plants is the very elementary method 

 of development of the cryptostomata ; and although no true conceptacle is 

 formed with special lining cells, such as occurs in the higher Fucacece, yet 

 the growth, both of the hairs and reproductive organs is initiated by the 

 alteration in form and by the division of one of the epidermal cells, which 

 might with truth be called an ' initial cell.'* 



To leave this statement without a qualification would not, however, be 

 exact, since my observations do not exclude the possibility of the initiative 

 being taken by a small group of initial cells dividing simultaneously, 

 instead of a single one. Whether the decision of this point may ultimately 

 prove to have a bearing on the affinities of such organs with the 

 cryptostomata of the Fucacece is one that at present I am unable to 

 determine. 



MARGARET O. MITCHELL. 



* Bower, Quart. J our ti. iVicr. Sa., vol. 



