the Anatomy of the Gentis Selaginella . 499 
vascular bundle of which the xylem consists of only eight to nine tracheides 
having only one protoxylem. 
The negative heliotropism of both types of roots has been studied in 
Fig. III. 1, cross-section of root of IVildenoivi ; 2 (a-e), development of root of same species ; 
3-9, S . grandis ; 3, aerial root without root-hairs or root-cap; 4, aerial root from * downward with 
root-hairs and root-cap ; 5, branch developed in extreme moisture, * branch instead of rhizophore, 
which has formed an aerial root ; 6, cross-section of rhizgphore ; 7, part of rhizophore with root-hairs ; 
8, cross-section of branch which is in the place of rhizophore; 9, root with root-cap and root-hairs. 
S. K raussiana , S. Wildenowi, S. rubella , molliceps , 5. pallida , 5. serpens , 
and vS. inaequalifolia. Young shoots of these species were turned upside- 
down ; the very young aerial roots soon turned in the opposite direction to 
L 1 a 
