THK VOL' NO SI'OKOPHYI 1 



157 



Daneea, e.g., /). elliptica; but in I), jenmani and in I), ^amatcensts, as well as in 

 most of the other species, the stem finally becomes dorsiventral, as it is from the 

 firsr in Kaulfussia. 



The development of the second leaf is marked by an increased activity in the 

 apical meristem, quite close to the apical cell, and it is clear that the leaf arises from 

 the younger segments, but it is impossible to state exactly what the relation of the 

 young leaf is to the younger segments of the apical cell, or to say whether the whole 



Fig. 141. 



A-C. Three transverse sectiuns of primary root of Mtirattia douglatii. 

 D Longitudinal section of apex of primary root. 



of the leaf is the derivative of a single segment. When the young leaf can first be 

 distinguished it is elevated very slightly above the level of the stem apex and its 

 growing point is composed of a group of columnar cells. Sometimes, especially in 

 Datura, there may be recognized near the center of this group of cells a single, 

 somewhat larger one, which may be interpreted as a single apical cell, but this is not 

 always recognizable. 



Fig. 142. 



A, longitudinal, M. transverse, sections of apex of primary root of Kaulfussia. X200 



C. Apex ot second root. 



D Transverse section of root apex. 



Even before there is any noticeable projection ol the leaf rudiment, then is 

 developed beneath it the beginning of the short strand of procambium which is to 

 form its vascular bundle, and this can be followed downward to a point below the 

 stem apex, where it joins the trace from the cotyledon. Above this junction there is 

 no evidence of procambium tissue extending into the stem apex, but the whole 

 tissue lying between the junction of these two primary vascular bundles and the 

 apical meristem of the stem is made up of undifferentiated parenchyma. 



The outer surface of the stem apex may be nearly horizontal or (especially in 

 Angiopteris) it may be strongly inclined and a single fairly conspicuous initial cell 



