144 



MANUAL OF BOTANY 



pith. It can be distinguislied from the latter by the fact that 



there is an endodermal band on both sides of the ring of bundles. 



The bundles are concentric in all four 



Fig. 901. genera. Thefundamentaltissuecoutains 



large intercellular spaces or lacunse. 



The growth in length of both stem 

 and root is carried on by means of an 

 apical cell, which is either two-sided or 

 tetrahedral. 



A curious feature of the leaf of 

 AzoUa is the occurrence of a pit or 

 cavity in the tissue of the dorsal lobe 

 in which small colonies of Nostoc fila- 

 ments are found, much as in Antho- 

 ceros. This is a case of symbiosis, as 

 in the latter plant. 



The two orders Salviniacese and 

 Marsileacese differ from each other in 

 the arrangement of their sporangia. 

 They agree in having them placed in 



Fig. 902. 



Fig. 901. Plant of Marsilea. k. ELizome. &. Leaves. /. Sporocarps 

 springing from the leaf stalks at a-. After Sacbs. — Fig. 902. Stele of ■ 

 Marsilea, showing gamostelic structm-o. a. Outer endodermis. &. Inner 

 endodermis. c. Fused xylem bundles. (/. A point at which the fusion 

 does not extend to the wood. e. Fundamental tissue isolated by the 

 fusion of the steles. /. Cortes. 



curious globular or ovoid bodies, which occur in Salvinia and 

 Azolla on the submerged leaves or lobes of leaves ; in Marsilea 



