818 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
to different natural orders. Even 1 in the young condition cotyledons 
exhibit three well-differentiated kinds of tissue — a rudimentary epiderm, 
a rudimentary parenchyme, and procambial bundles. The epiderm 
always consists of closely fitting cells of a smaller radial diameter than 
those of the parenchyme. The parenchyme is usually composed of several 
layers of isodiametrical cells. The procambial bundles consist of narrow 
elongated thin-walled cells fitting closely together. With the exception 
of the underground cotyledons of non-albuminous seeds, such as those of 
Pisum and JEsculus , most cotyledons have the power of growth ; and 
this growth depends chiefly on the increase in size of the individual 
cells and their separation from one another, rather than on cell-division. 
As contrasted with foliage-leaves, cotyledons have usually a larger 
number of layers in the mesophyll ; their mechanical elements and the 
conducting system are less developed ; the epiderm is less sharply 
differentiated ; the number of cotyledons is usually smaller in proportion 
to the area, and they are more uniformly distributed on the two sides. 
Leaves of Iridese.* — Prof. R. Chodat and Mdme. G. Balicka-Iwa- 
nowska have studied the structure of the leaf in a number of genera of 
IrideaB. The leaf of Boumulea , although resembling that of Crocus in 
appearance, is, in reality, of the equitant type characteristic of most 
genera of the order. The epiderm is always composed of only a single 
layer of cells, the external wall of which is often furnished with cuti- 
nized pearls. The stomates have always four guard-cells, and the form 
of the cells is very uniform throughout the group, with a few exceptions. 
The hypodermal vascular bundles constitute a very characteristic tissue 
consisting of elongated prosenchymatous cells with thick walls and 
oblique striae. The IxieaB are distinguished from all the other genera 
by having a true mid-rib. It is rare to find in the order any true 
palisade-tissue. 
Cells bordering the Guard-cells of Stomates. f — Herr W. Benecke 
describes the structure of the epidermal cells which he distinguishes as 
“ Nebenzellen,” i. e. those cells bordering the guard-cells which differ 
considerably in form from the others belonging to the epiderm. The 
leaves examined were mostly more or less of a succulent character ; and, 
after a minute description of the stomatal arrangement in a number of 
different natural orders, the author classifies the examples investigated as 
follows : — A, Stomates without border-cells ( Sedum pentJiorum, Subularia 
aquatica , many Orchideae) ; B, Stomates with border-cells ; I. Type of 
succulents contracting on loss of water ; a , the contraction takes place 
in all directions ; a, 3 border-cells surround the guard-cells in all 
directions (Crassulaceae, PlumbagineaB except Armeria, Urticaceae, 
Begoniaceae, Gesneraceae, Stapelia, Cruciferae, Violaceas) ; /?, 2 border- 
cells ; either the stomate is parallel to the ideal axis of division (Portu- 
lacacese, Mesembryanthemuin , Chenopodiaceae, Asclepiadeae except Sta- 
pelia , Cactaceae, Euphorbiaceae), or at right-angles to it (Labiatae, 
Acanthaceae, Caryophyllaceae, &c.) ; y, 4 border-cells ; either forming a 
* Journ. de Bot. (Morot), vi. (1892) pp. 220-32, 253-67 (1 pi. and 13 figs.). 
Cf. this Journal, ante , p. 385. 
t Bot. Ztg., 1. (1892) pp. 521-9, 537-46, 553-62, 569-78, 585-93, 601-7. 
