144 



MANUAL OF BOTANY 



pith. It can be distinguished 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. The fundamental tissue contains 



large intercellular spaces or lacunae. 



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 

 Azolla 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 Salviniaceae and 

 Marsileaceee differ from each other in 

 the arrangement of their sporangia. 

 They agree in having them placed in 



Fig. 902. 



Fig. 901. Plant of ilarsilea. k. Rhizome, h. Leaves. /. Sporocarps 



springing from the leaf stalks atx. Alter Sachs. /'/</. 902. Stele of 



Marsilea, showing gamostelic structm-e. a. Outer eudodermis. h. Inner 

 endodermis. c. Fused xylem bundles, d. A point at which the fusion 

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

 fusion of the steles. /. Cortex. 



curious globular or ovoid bodies, which occur in Salvinia and 

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



