xii LEPTOSPORANGIAT.E HETEROSPORE.E 389 



first, and only later attains its permanent form. The root 

 remains undeveloped, and no later ones are produced, but the 

 first divisions in what corresponds to the root quadrant in Azolla 

 are apparently very similar to those of that plant, and it would 

 perhaps be more correct to say that the primary root remains 

 undeveloped rather than to consider it as completely absent.^ 



The second leaf in the embryo oi Azolla arises practically from 

 the first segment of the stem apex, and each subsequent 

 segment also produces a leaf. The early growth in length of 

 the primary root is slow% and it does not become conspicuous until 

 a late stage. The vascular bundles are poorly developed and 

 arise relatively late. No trace of them can be seen until the 

 second leaf is well advanced. Their origin and development cor- 

 respond to those in other forms described. The tracheary tissue 

 is composed entirely of small spiral tracheids. 



The second root arises close to the base of the second leaf, 

 and like all the later ones is of superficial origin. As the 

 cotyledon grows, large intercellular spaces form in it, and the 

 young sporophyte breaks away from the spore or carries the 

 latter with it to the surface of the water. As the embryo breaks 

 through the episporic appendages at the top of the spore, these 

 are forced apart and the cap-shaped summit of the indusium is 

 thrown off. The cotyledon is funnel-shaped, with a cleft on one 

 side, and completely surrounds the stem apex. The root is still 

 conspicuous, and forms only a slight protuberance upon one side 

 of the foot, which looks like a short cylindrical stalk (Fig. 200). 



The growth of the first root is limited, and it differs from the 

 later ones by forming peculiar stiff root-hairs. The later roots, 

 except the second, do not seem to bear any definite relation 

 to the succeeding leaves. 



A careful examination of the ripe macrosporangium shows 

 a number of colourless small round bodies occupying the space 

 between its upper wall and the indusium. These are the resting 

 cells of a nostoc-like alga — Anabcena Azollce, — which is always 

 found associated with this plant. At the same time that the 

 embryo begins to form, these cells become active, assume the 

 characteristic blue-green colour of the growing plant, and divide 

 into short filaments that at first look like short Osdl/aricB. The 

 cells soon become rounded, and heterocysts are formed. Some 

 of these filaments remain entangled about the stem apex of the 



1 Dutailly (I). 



