184 PROCEEDINGS OF THE AMERICAN ACADEMY 



peu rcservee en pointe a son sommet puis eiisuite lineaire sur la 

 plus graude partie de sa longeur, s'amiucit successivement jusqu'a se 

 terminer par uu petit stipe presque capillaire, oil Ton distingue ' 

 neanmoins, au dessus de son point radical, I'espece de petit noeud 

 (Rhizogene), que j'ai vu plus tard s'accroitre et donner naissance aux 

 priucipales raciues qui fixent cette Algue aux corps solides." It is 

 very evident from this description that De la Pylaie recognized this 

 swelling just above the {jrimitive discoid attachment as well as its 

 function, and that he gave to it the name of " Rhizogene." In regard 

 to this organ and the term applied to it, he explains in a foot-note as 

 follows : " Organe exclusif a cette hydrophyte et au L. bulbosa ; il 

 n'existe que chez ces especes dans tout le regne vegetal ! n'ayant pas . 

 encore ete dcsigne par un nom particulier, je propose celui-ci dont je 

 me servirai pour eviter periphrases." This name, Anglicized to rhizo- 

 gen, will be adopted in this paper to designate this organ. The blade 

 in specimens in this stage varies from 3.5 cm. to 6.5 cm., and is per- 

 haps at times even longer. It is narrowly cuneate at the base, 

 and still bears some traces of the primitive blade at the apex (of. 

 Fig. 4, E). 



2. Development of the First Hapteres. — For a number of stages 

 now the changes which take place in the rhizogen are of particular 

 interest. It increases, chiefly in diameter, until it projects out around 

 the stipe in the form of a circular ridge, as shown in Figure 5 at B. 

 This specimen is 7.3 cm. long. The holdfast is a disk-shaped body 

 about 2 mm. in diameter. It will be best hereafter to distinguish this 

 first organ for attachment to the substratum as the primitive disk or 

 primitive holdfast. The rhizogen is situated about 2 mm. above this, 

 and forms a conspicuous projecting circular ridge, about 3 mm. in 

 diameter. Its upper surface is convex and rounded, while the lower 

 surface is concave to a slight extent. Its projecting edge is coarsely 

 crenate into five small lobes. The stipe in this specimen is 7 mm, 

 long and 1.5 mm. in diameter. The base of the lamina is narrowly 

 cuneate, as in the precedhig period, but the blade itself is more lance- 

 olate, occurring very linearly lanceolate in some specimens. A trace 

 of the primitive blade (cf. Fig. 5, E) still lingers in some specimens. 

 The cryptostomata are very abundant in this stage. 



As the plants increase in size the rhizogen continues to grow. It 

 increases in diameter proportionally with the stipe. The lobes, scarcely 

 noticeable at the beginning, grow out into finger-like processes (cf. 

 Fig. 6, F), which extend out at first nearly horizontally, and then 

 more and more obliquely downwards. Figure 6 represents a specimen 



