LEAVITT: TRICHOMES OF ROOT. 
305 
ledons. It is hence possible that the short exodermal cells of the 
Dicotyledons are strictly homologous with the trichoblastic elements 
of the epidermis of Monocotyledons. Assuming that both sorts of 
structure have had a common origin, the short hypodermal cells of 
the Dicotyledons may be regarded as potential trichomes, the tri- 
chomic development of which is prevented by the persistence of a 
sheath, the epidermis, derived from the root-cap. When this sheath 
fails, as in Nymphaea, the short cells then reveal their primitively 
trichomic character by resuming their proper development. 
Whichever structure may have been the primitive one in the 
earliest Angiosperms, there seem to be grounds for regarding the 
differentiating process as one and the same whether it affects the 
epidermis or the exodermis. 
The systematic distribution of transfusion cells of the exoderm. 
— Oudemans, Leitgeb, and De Bary observed a large number of 
cases in aerial roots of Aroideae and Orchidaceae. The list given 
below is that of Juel, augmented by instances which have come 
under my own observation. The latter are starred. 
Liliaceae : Agapanthus umbellatus, Allium narcissiflorum* A. 
Schoenophrasum, Anthericum Bernarnii * Artliopodium pan- 
iculatum, Brodiaea congesta * Chlorophytum iSternbergianum , 
Bianella coerulea , I). stricta, Funckia land folia, F. ovatafl 
Hemerocallis fulva , Phormium tenax , Scilla peruviana, 
Veltheimia capensis, Xanthorrhoea arborea, Xerotes fluviatills, 
X longifolia , Yucca angustifolia , Y. Draconis. 
Convallariaceae : Asparagus truophynus* A. verticillatus, Conval- 
laria majalis, C. multiflora, C. polygonatum, Cordyline 
stricta * Dracaena cannaefolia , D. Draco , D. rubra , Maianth- 
emum bifolium, Paris quadrifolia, B use us Hypoglossum , R. 
aculiatus, Semele androgyna, Srnilacina stellata, Arnilax 
herbacea. 
Amaryllidaceae : Agave densiflora, Amaryllis amethystinus, A. 
Bellado7ina, A. vittata , Amorcliis longifolia, Olivia miniata, 
C. nobilis, Crmum asiaticum, C. bracteatum , Doreanthus 
Paimeri, Eucharis amazonica, Galanthus nivalis, Haemantlius 
puniceus, ITymenocallis caribaea , Ilypoxis erecta * Xarcissus 
poeticus, X. tazetta, Pancratium maritimum, P. ovatum* 
Sprekelia formosissima , Yallota purpurea. 
