12 MINNESOTA BOTANICAL STUDIES. 



not retain the cortical structures in place, but gave excellent re- 

 sults in the dense medullary region. Preparations were made 

 also by imbedding the material in paraffin, and sectioning in 

 the usual manner. By this means sections 6.66 microns in 

 thickness were obtained. They were of little value in study- 

 ing the vegetative tract, on account of the loose nature of 

 the tissues involved, and the great shrinkage of the gelati- 

 nous matrix incident to this process, but they gave excellent 

 preparations for the study of the later stages in the development 

 of the cystocarp. 



Gross Anatomy. In the most perfect specimens the frond is 

 vermiform and much branched (Fig. /) About six main branches 

 arise from a small disc-shaped holdfast. These main branches 

 are repeatedly branched, pinnately and also dichotomously, and 

 the ultimate branches are often furcate a short distance from the 

 tip. The extreme length from the holdfast to the tip of the 

 longest branch is 20 cm., the average height of the frond about 

 15 cm. The branches are 1-3 mm. in diameter, almost cylin- 

 drical, tapering gradually to about .5 mm. in diameter at the 

 obtuse tip. The branches are very mobile and yield freely to 

 the slightest motion of the water. 



The whole thallus is gelatinous, and all parts of it, except 

 the youngest growing portions of the branches, contain a con- 

 siderable quantity of calcium carbonate which forms a white 

 granular sheath about the medullary portion of each branch, 

 and is itself surrounded by the outer cortical portion. Accord- 

 ing to the collector the color of the fresh frond was brownish- 

 red, but all trace of color had disappeared in the preserved 

 material. 



Minute Structure of the Vegetative Tract. The frond 

 consists of two areas, a medullary portion and a cortical layer 

 (Plate V.,Fig. 6). Throughout the frond the filamentous struc- 

 ture of the tissues which is common among the Rhodophyceae may 

 be clearly distinguished. The filaments of cells lie imbedded 

 in a general thin gelatinous matrix which is formed by the coal- 

 escence of the swollen gelatinous outer covering of the cells. 



The medullary region consists of intermingled longitudinal 

 filaments of two distinct types (Figs. 6, 7). The larger fila- 

 ments are the primary filaments of the frond, and all other 

 parts are derived from their lateral branching. They are com- 

 posed of cells 120-1,300 mic. long and 12-120 mic. wide. 



