Dar bishire. — Observations on Mamillaria elongata. 385 
The cells of the ground-tissue are parenchymatous throughout. 
Immediately inside the epidermis is found an hypoderma ( d ), consisting of 
flat, short cells, which really differ only in form from the next inner cells. 
They usually contain a few chloroplastids. Except near the stomata, they 
leave no intercellular spaces between themselves and the epidermis. 
These cells are succeeded by rows of palisade-cells, which run parallel 
to one another and make a definite angle with the epidermal layer ; each 
row consists of 2-6 cells. Very extensive and continuous air-spaces are 
found in connexion with these rows of cells. They seem often to completely 
surround the palisade-cells, so that these appear to be like the assimilating 
filaments in Marchantia , namely, loose threads. This is, however, not 
actually the case. They represent the chief assimilating cells of the plant 
and contain therefore very many chloroplastids. These are round in form 
and measure 5-7 \x across. I have nearly always found the chloroplastids 
applied to the two walls which run parallel to the longitudinal axis of the 
filaments, at other times they closely surround the nucleus. Most of the 
remaining inner part of the ground-tissue consists of large roundish cells, 
with but few chloroplastids. Some of these cells, more particularly nearer 
the apex of the wart, contain large crystals of calcium oxalate. The 
ordinary round ground-tissue cells pass into the filamentous palisade-cells 
very abruptly. 
A number of parenchymatous cells are enclosed in the cup-like ending 
of the vascular tissue. They are almost colourless, clear cells, and also 
frequently contain large quantities of calcium oxalate. 
Of very great interest is the ending in the tubercle of the vascular 
system. This is a very highly developed structure, and it alone would show 
that M. elongata represents a very high degree of adaptation to external 
conditions. 
The bundle-system of the tubercles is of course connected with that of 
the main stem. The arrangement met with is that described by Ganong 
for those Mamillariae which have no furrows on the upper side of the 
tubercles (10, p. 35, Fig. 14). From Ganong’s observations and from my 
own it appears that one strand of vascular tissue leaves a bundle of the main 
stem for every tubercle (PI. XXV, Fig. 3). This bundle is about 1 20-150 [i 
thick and it originates in the inner end of one of the stem-bundles. It 
consists in fact of part of the protoxylem and part of the metaxylem and 
the phloem. On leaving its parent bundle it passes between the two 
bundles to the cortex, rising slowly in a direction towards the tubercle. 
From this one lateral bundle are derived the bundles of the cortex of the 
main body of the plant, the bundles of the tubercle and those of the lateral 
bud, which is found in the axil of each tubercle. According to Ganong the 
bundles of the assimilating tubercle consist of a leaf and a cushion system 
of bundles fused. It is quite immaterial here what their morphological 
