304 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Oudemans demonstrated the distinctive chemical nature of the 
membranes of the short cells (Oudemans, l. c.). In sections treated 
with sulphuric acid and iodine, the elongated prismatic cells remained 
brown while the short cells stood out as alternating areas of blue, 
(cellulose reaction). Attention has been called above and in accom¬ 
panying figures to the projection of the short cells. In Eucharis 
amazonica the communication of the short cells with the exterior 
is, in the older parts often direct. 
The evidence from structure, therefore, indicates that the short 
cells of the exoderm have, in common with the short cells of the 
epidermis, an absorptive office. 
The systematic distribution of the two phenomena under consid¬ 
eration is of interest. They are rarely found together (Monstera 
deliciosa, Anigozanthos pulcherrima ). As will be seen from the 
list of species given below r , special transfusion cells of the exoderm 
occur in those groups of the Monocotyledons which are without 
predetermined hair-cells. They are found also in many Dicotyledons. 
These facts of anatomy, physiology, and distribution lead to 
speculation upon the morphological equivalence of the two sorts of 
cells. It may be surmised that they express the same original forma¬ 
tive, structural principle. If the tegumentary structure prevailing 
in a large number of groups of Monocotyledons and in the higher 
vascular Cryptogams may be taken as the primitive condition, char¬ 
acteristic of the ancestry of the Monocotjdedons, we may suppose 
that in the instances enumerated below (exclusive of the Dicotyle¬ 
dons) the tendency inherent in the epidermis to form trichoblasts 
has passed over to an underlying layer which histogenetically is 
closely related to the epidermis. This transference, it may be sup¬ 
posed, was effected in the modification of the tegumentary apparatus 
which we see in the groups in question, a modification necessitated 
by the epiphytic habit (Orchidaceae, Aroideae), or by life in the 
drier soils where periodic or occasional droughts are encountered 
(the majority of the Liliifiorae). 
In the Monocotyledons the superficial layer of the young root 
(epidermis) is morphologically a cortical member. In Dicotyledons 
the epidermis has its origin in common with the root-cap ; and the 
exoderm, therefore, the layer which in many Dicotyledons is char¬ 
acterized by the differentiation of transfusion cells—is the outer 
cortical layer, homologous with the external layer of the Monocoty- 
