FILICINEAE. HETEROSPOROUS FILICINEAE. 



235 



longitudinal rows of cells, which proceed from two rows of segments ; the two 



dorsal rows are sterile and produce neither leaves nor buds ; the two rows of 



leaves are formed from one right and one left row of the dorsal half, and the 



branches from the two neighbouring rows of cells of 



the ventral half of the stem, in front of or behind 



the leaves; lastly, the two lower ventral rows form 



roots, each of which arises beside (under) a bud 



and developes by means of a three-sided apical cell. 



If in the Fig. 188 we suppose the leaves marked 



L z to be the only ones present, we get very nearly 



the arrangement of the leaves in Azolla in which 



the dorsiventrality is shown by the position of the 



leaves on the dorsal or upper face, the lateral buds 



on the lateral faces, and the roots on the ventral FIG - l88 ' Diagram of the leaf-arrange- 



ment of Salviuia natans. The side marked 



face. The roots have this interesting peculiarity, wi ! h the letters vo is the ventral side. Each 



' ' pair of aerial leaves and one submerged leaf 



that they after a while cast off the root-cap and are inserted at "= same height on the 



* young stem. The submerged leaf w is 



so come to be iust like the submerged leaves of form ednrst, then the aerial leaf ,, last the 



J aerial leaf L 2 , and so on. After Pnngsheim. 



Salvtnid 1 . 



In Marsilia the segmentation of the apical cell in three rows is maintained even 

 in the grown plant ; one row of segments comes to be below and ventral, the two 

 other rows form the dorsal face of the stem. The ventral side of the stem gives off 



FIG. 189. Summit of the horizontal floating stem of Salvinia. A inferior or ventral side. /? left side. C transverse 

 section of the elongated vegetative cone ; .SS apical cell of the stem, y last division of the apical cell, -w submerged leaf, 

 Z its lateral teeth, L\ , LI the aerial leaves, h h the hairs. After Pringsheim. 



roots in strict acropetal succession, as in Azolla ; the youngest is found at the apex 

 of the stem : the leaves are formed on the dorsal side of the stem in two alternating 

 rows, since certain dorsal segments are sterile and serve to form internodes. The 

 first leaf of the embryo, which has no lamina and is placed in the median line, 

 is followed in the arrangement in two rows, which is now commencing, by a number 

 of juvenile leaves with short stalks, and with the lamina at first entire, then divided 



1 Westermaier u. Ambronn, Eine biolog. Eigenthumlichkeit d. Azolla caroliniana (Verb. d. hot. 

 Vereins d. Prov. Brandenb. 1880). 



