No. 7. — TRICHOMES OF THE ROOT IN VASCULAR 
CRYPTOGAMS AND ANGIOSPERMS. 1 
BY ROBERT GREENLEAF LEAVITT, A. M. 
Contents. 
Page. 
Two types of trichomes of the root recognized.273 
The first type characterized.274 
Distribution.274 
Filices.274 
Hydropterideae — Marsilia.275 
Monocotyledons .. 275 
Dicotyledons .277 
Trichomes of the second type described.279 
Distribution—general .......... 283 
— in detail.283 
Filices.284 
Hydropterideae — Azolla.284 
Equisetinae.285 
Lycopodinae.•.286 
Monocotyledons.290 
Dicotyledons .300 
Transfusion cells of the exoderm.301 
Origin ............. 301 
Similarity to trichoblasts.303 
Morphological equivalence of transfusion cells and trichoblasts . . 304 
Systematic distribution of exodermal transfusion cells . . . 305 
Concluding remarks ..306 
Two Classes of Radical Trichomes. 
The trichomes which arise in the superficial layer of the root of 
vascular plants as organs of absorption are of two types. Tri¬ 
chomes of one kind result from a differentiation of the meristematic 
cells of the young epidermis near the apex of the root; those of the 
other class have a simpler origin. The more commonly recognized 
and less highly specialized type will be first described. 
1 Contributions from the Ames botanical laboratory, no. 2. 
