FILICINE^. 



451 



segments in two rows are at first formed from it by walls inclined upwards and 

 downwards ; the dorsal median leaf also proceeds from the first dorsal segment. 

 But a different arrangement is soon produced as the plant increases in strength; 

 the apical cell of the stem forms segments arranged in three rows with a J diver- 

 gence, and in such a manner that one row of segments comes to lie below (ven- 

 trally), while the two other rows form the dorsal side of the stem. The ventral side 

 of the stem forms roots in strictly aero petal succession, as in Azolla, the youngest 

 being found near the apex of the stem. On the dorsal side of the stem the 



Fig. 317.— Anterior part of the stem oi Marsilia 

 Salvatrix with leaves (reduced one-half) ; A' terminal 

 bud. b b leaves.y/sporocarps springing from the leaf- 

 stalks at X. 



Fig. -^i^.—Pzlularta globitlt/era ; A natural size, B end 

 of a shoot magnified, s terminal bud of the stem, deleaves, 

 IV roots, /'sporocarps, A' lateral bud. 



leaves arise in two alternating rows, some of the dorsal segments remaining at 

 the same time sterile and serving for the formation of internodes. The first leaf 

 of the young plant, lying in the median line and without a lamina, is followed, 

 in the biseriate arrangement which now results, by a number of young leaves with 

 a short stalk and a lamina at first entire but afterwards divided into two and 

 four lobes ; normal leaves, circinate in their vernation, are then for the first time 

 formed with a long stalk and a quaternate lamina. In the processes which have 

 now been described, Pilularia agrees, according to Hanstein's observations, with 



G g 2 



