66 MINNESOTA BOTANICAL STUDIES. 



Of Valoniaceaj exposed to like conditions of wind and wave, 

 Dictyosph&ria needs more firmness. Valonia thalli, on ac- 

 count of their form and structure, need no support, and the re- 

 maining Valoniaceae gain sufficient cohesion through interlacing 

 branches. 



The presence of the needles may be due to the loose struc- 

 ture of the Dictyosphceria thallus, or to the necessity of having 

 an internal balance to the haptera. There is no stimulus to 

 growth from direct contact, as in haptera, and these may arise 

 from strain on older thallus. Whatever the function, it is sub- 

 sidiary to that of the haptera, as they are less numerous, and 

 chiefly in greater numbers in central cells. 



External cell strengthening. — Haptera or intercellular organs 

 of attachment are present in Udotea, Boodlea, Microdictyon 

 and Spongocladia, and bind one part of the thallus to another, 

 as in Struvea, where they fasten pinna to pinna, or one cell to 

 another as in Dictyosphceria. In all cases they bind a thallus 

 of loose structure together. 



Origin. — The origin of the haptera is due to the evagination 

 of about one third of the cell wall, similar to the invagination 

 in the case of the needles. 



Their primary importance as compared with the needles is 

 perceived, for they are never absent, and no young stages of 

 development are present. They are, however, formed through 

 a similar process, i. e., the evagination of the stratifications. 

 The cross beams, caused by stratifications, are nearer their tips, 

 thus leaving a larger lumen (PI. XV., -Fig. 10). 



Optical sections near the base appear as dark rings from one 

 to several in number, due to the number of main branches of 

 haptera which are present (PL XV., Fig. n). 



The haptera are hollow and have no contents. 



Development. — The evagination continues until a surface is 

 reached to give the needed stimulus. At this stage the haptere 

 consists of an unbranched tube ending in a closed blunt end 

 PL XV., Fig. ij). The tube or stalk now begins to lobe di- 

 chotomously, and the ends flatten out upon the wall. This 

 continues until a branched circle of lobes is formed, convex and 

 radiating (PL XV., Fig. id). The hollow space thus formed 

 between the opposite cell wall and the concave center causes 

 adhesion by sucking (PL XV., Fig. 14). The base shows from 

 one to three enclosed oval rings, due to the number of main 



