48 MINNESOTA BOTANICAL STUDIES. 



Material was also washed with water for twenty-four hours 

 and then passed through the alcohols before staining, but no 

 advantage was gained. The material treated with hydrochloric 

 acid differed only in that it showed a more distinct vacuolated 

 condition, which in the younger active pseudocysts was very ap- 

 parent. Many of these pseudocysts also showed a single very 

 large granule, but this may also be seen in the normal con- 

 dition. Nearly all the stained pseudocysts are constricted along 

 the middle region. 



Observations. 



The dark brown color of the stratum is due to the color of 

 the gelatinous sheaths in which the trichomes are imbedded. 



Filaments. — The filaments are not attached, yet the gravel 

 remained clinging to them when they were detached from the 

 bottom of the stream, due no doubt to the gelatinous nature of 

 the sheath. They seemed to lie horizontally and to be without 

 any definite arrangement. They are in general more or less 

 curved. Many of the filaments are without branches, but 

 pseudobranches are not at all uncommon. Branching occurs 

 either near a heterocyst or at a distance from it (see Figs, 5 and 

 6). In the first case there is but one branch, that is, the tri- 

 chome being broken off at the heterocyst is thrust out as a single 

 thread which soon secrejes a new sheath about itself. In the 

 latter condition both the broken ends of the trichome project, so 

 that there are two branches or twin branches. 



Sheath. — Harvey's description cannot be improved upon : 

 "When placed under the microscope the filaments present the 

 appearance of a cylindrical central column, containing annu- 

 lated, olive-colored endochrome and a wide, wing-like border 

 at each side of the column. This border or sheath is obliquely 

 striate, the striae running in an arch from the margin toward the 

 center, where they become parallel and are then continued 

 longitudinally downward along the medullary column till lost 

 in the density. The margin of the wing is closely crenulate, 

 and in age transversely striate at the crenatures as though 

 jointed. Such is the apparent structure ; the real structure 

 seems to be that an annulated central filament is enclosed 

 within a number of compressed, trumpet-mouthed gelatino- 

 membranaceous tubular sheaths, one arising within the otht-r 

 and successively developed as the growth proceeds. These 

 sheaths, thus concentrically arranged, are indicated by arching 



