Butters: observations on trichoglcea lujbrica. 13 



These cells are widest in their median portion, and are usually 

 constricted at the ends. In the older portion of the frond they 

 becomes highly vacuolate and finally almost devoid of contents, 

 so that only the cell wall is capable of taking any appreciable 

 stain. 



Filaments of this type are occasionally unbranched for a con- 

 siderable distance, but usually each filament gives rise to a 

 series of lateral branches, of which one arises near the upper 

 end of each cell of the filament. Occasionally, one of these 

 lateral branches runs parallel to the parent filament to which it 

 is in all respects similar, and so forms an additional medullary 

 filament, but in most cases the lateral branch passes out per- 

 pendicularly into the peripheral region of the frond, and gives 

 rise to a branch system of cortical filaments {Figs, j, 5). In 

 mature portions of the frond the primary filaments are often 

 crowded together in the outer medullary region, forming a rather 

 irregular hollow cylinder, within which are other more widely 

 scattered primary filaments {Fig. 6). 



Besides these larger filaments there are smaller filaments 

 which run irregularly among the larger filaments {Fig. 7). 

 These smaller filaments are composed of cells 45-140 mic. 

 long, and 4-10 mic. in diameter, and the filaments are of nearly 

 uniform diameter throughout, in which respect they differ from 

 the larger filaments as well as in size. Their protoplasmic 

 contents are more dense than those of the larger filaments. 



These smaller filaments branch sparingly. They arise by 

 the secondary branching of the cortical filaments, as will be 

 described in detail in connection with the structure of the 

 cortical portion of the frond. 



The cortical area of the mature frond is composed of a com- 

 plex branch system of filaments {Figs. 4, 5), and may be divided 

 approximately into two regions, an outer or assimilating area, 

 which forms the surface of the frond and consists of compara- 

 tively simple moniliform filaments, and an inner area which 

 lies between the medulla and the assimilating area, and con- 

 sists of intricately interwoven filaments of complex branching 

 habit. 



To appreciate the structure of the cortical area, its develop- 

 ment must be understood. Examination of the growing point 

 of the frond shows the dense medullary region, which here 

 consists entirely of the large primary filaments, and surround- 



