48 BOTANICAL GAZETTE [JULY 
it firmly to the ground, but only to a slight degree prevents a 
swaying movement, easily induced, even in plants 1.5™ high, by 
comparatively little force. Hence to the large lateral roots, 
developed from the sunken base at a later period, is given the 
function of steadying the whole plant, in addition to their pri- 
mary work of absorption. 
MAMILLARIA GRAHAMI Engelm.—The epidermis is free from 
crystals, but the one-layered hypoderma contains them in almost 
all its cells. The assimilative tissue is of small cells elongated, 
as usual, perpendicular to the surface. The colorless medullary 
portion is of thick-walled cells pitted as in &. Wishzeni and 
C. giganteus, and grades into the assimilative tissue. The lateral 
bundles can here be traced out into the tubercles. The stem 
bundles appear to start in a more or less wavy line, and to suffer 
fusion to some extent. There is comparatively little branching, 
but secondary medullary rays are occasionally found, and there 
is also a growth of the bundles in width, so that finally a rather 
compact cylinder is formed. As regards branching and internal 
structure of bundle, this species approaches C. Fendleri nearer 
than any of the others. The xylem is composed of alterna- 
ting portions of spiraled ducts and tracheids of the flattened- 
spiral type, the latter being the more prominent. The phloem 
has a slight compressed sheath of sclerenchyma. Sieve tubes 
appear rather poorly developed, a_ thick-walled, somewhat 
elongated parenchyma taking up most of the region of the 
phloem. 
In this small species there is apparently no distinction of 
anchoring and absorptive root systems. The bundle cylinder is 
compact, the pith practically absent, and the medullary rays 
reduced generally to a single cell layer. The phloem is slight 
and of sieve tubes. Outside the phloem, filling the small space 
between it and the cork cambium, is a parenchyma tissue of large 
rather thick-walled cells. The xylem consists chiefly of spiraled 
tracheids, with some amount of extra reticulation, and of smaller 
ringed ducts, the rings flattened inward, sometimes also bound 
together by extra spirals or reticulations. Crystals occur but 
