XI 



LEPTOSPORANGIAT^ HETEROSPORE^ 



407 



ing to Leitgeb/ the apical cell of the stem is always three-sided 

 at 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 (Dutailly (i)). 



The second leaf in the embryo of 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 



B 



Fig. 237. — Azolla Ulicidoides. Nearly median section of the young sporophyte after it 

 has broken through the prothallium, Xioo; B, an older plant with the macrospore 

 (sp) still attached; m, massulae attached to the base of the macros^pore; r, the 

 primary root, X40. 



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 w^ell advanced. Their origin and develop- 

 ment correspond 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 coty- 

 ledon grows, large intercellular spaces form in it, and the young 



'Leitgeb, see Schenk's "Handbuch der Botanik," vol. i. p. 216. 



