M. Midler on the Germination of Isoetes lacustris. 183 



solution. It does not wholly disappear until the time when the 

 second leaflet emerges from the vagina and acquires a green 

 colour. Then the cells of the alimentary body which have step 

 by step become looser and more transparent are found quite 

 empty (figs. 22 c, 23 c), and their membranes of a brown colour. 

 I have never observed them to become again filled with any 

 kind of matter. It appears to me probable, that we have here, 

 on a small scale, what afterwards happens on a large one in the 

 rhizome of Isoetes, where the outermost layers, so soon as they 

 have fulfilled their functions in the service of the leaves, when 

 these decay are also destroyed, since they are then to be met with 

 only as a brown spongy tissue forming the brown lamellse on 

 each side of the rhizome. 



2. The Matrix of the Root. — Although it is impossible to per- 

 ceive where the first root will be developed, in the stage where 

 the matrix and the alimentary body have exactly the same form 

 (fig. 15 c,f), there is no doubt about the matter in the stages of 

 development which soon succeed, since the root now unfolds very 

 rapidly. 



In this we find conditions exactly opposed to what occur in 

 the alimentary body. The matrix of the root is composed of the 

 same small parenchymatous cells. As in that, these originally 

 possess distinct cytoblasts. But unlike what we found there, 

 these do not become transformed into starch, but are dissolved 

 at once into an almost transparent cytoblastema. This is the 

 first stage of the development of the root ; by this the matrix 

 obtains nutrient matter, by means of which its further unfolding 

 is rendered possible. The formation of new structures takes 

 place here, as may usually be seen very distinctly in all rootlets, 

 at the apex. And it must be noticed that the cytoblasts are first 

 dissolved at the very apex of the matrix, this process gradually 

 extending to the remaining portion (fig. 17 e, g). The primordial 

 cells of the apex of the rootlet, which are of extremely delicate 

 texture, appear empty at this stage. 



An important alteration soon succeeds. All the cells of the 

 matrix are empty, while this has become elongated gradually and 

 in such a manner that the apex appears rather thin and the back 

 part thicker and club-shaped (fig. 18 e). The most external layer 

 of the cells of the matrix may also be easily distinguished from 

 the internal. The former have become firmer and inclose the 

 latter as an epidermis. It is striking here that the cells of its 

 extreme point contain cytoblasts within them (fig. 18y). 



The most essential change however that occurs in this stage is 

 the first appearance of the vessels (fig. 18/). These emerge as 

 two short cords from the interior of the alimentary body, and I 

 have never been able to discover the point whence they originate. 



