Crosby : OBSERVATIONS ON DICTYOSPHLERIA. 67 



branches (PL XV., Fig. //). The main tubes may develop 

 lobes directly (PL XV., Fig. //), or may become branched 

 from one to three times in various directions and levels (PL 

 XV., Figs, ii and 12). Each branch then develops (PL XV., 

 Fig. n) a separate system of radiating lobes, as seen in cross- 

 section, central view (PL XV., Fig. 12). As before, the con- 

 ditions determine size and shape. The haptera are absent from 

 the outer walls of external cells of the thallus, but are abundant 

 elsewhere, and often crowded when developed from the larger 

 cells (PL XV., Fig. 11). Near the exterior, the closely con- 

 nected cells cause the haptera to be short-stalked, and after the 

 opposite wall is reached, continued branching occurs over a 

 varying area, limited only by contact with neighboring haptera. 

 In the central cells, longer stalks arise from the separated cells. 

 In the intercellular spaces their length is often much greater, 

 induced by the greater space (PL XV., Fig. if). A haptere 

 near the edge of the intercellular space is often two or three times 

 branched, and clasps the surfaces in various directions, to meet 

 the added strain at this position (PL XV., Fig. //). The 

 haptera generally extend directly to the opposite cell wall and 

 thus the base from cell I alternates with the lobes of cell 2, but 

 they also extend diagonally and at different levels (PL XV., 

 Fig. //). The numbers, size of the haptera, length and direc- 

 tion of tubes, number of branches, area of adhesion and posi- 

 tion, depend on the distance between the cells. 



Rhizoids. -T\\t rhizoids, centrally situated, are elongated, 

 unicellular structures, and are developed from the ventral sur- 

 face of the thallus. They show little differentiation and corre- 

 spond to the normal plant cells. They function as primitive 

 holdfasts, attached to the underlying surface of coral, and are 

 thallus cells, enlarged, elongated, irregularly shaped, and, 

 rarely, budded. To strengthen attachment to substratum, 

 haptera, similar to those above described, are formed from the 

 outer edge of rhizoids. These are few in number (PL XV., 

 Fig. 75).' The relation between the strength' of the rhizoids 

 and the position of the plant is intimate, their function being 

 aided by secondary structures, the haptera. The color is 

 generally a strong green, rarely reddish. 



The cell wall in form and structure is similar to that of thal- 

 lus cells. In arrangement the rhizoids are scattered or massed 

 together. In size they vary greatly, the longest five mm. by 



