Anatomico-physiological Relations in the Spermophyte Shoot . 163 
anthocyanin is usually present in, the innermost layer of the cortex, and 
also, though to a less extent, in the outermost layer, the intervening layers 
and the epidermis being colourless. Now in this species adventitious buds, 
from one to three or four in number, are frequently formed in the lower 
region of the hypocotyl and develop into branches. These buds are 
exogenous in origin and are derived from the epidermis and first hypodermal 
layer (see Figs. 28 and 29). In a hypocotyl containing so little anthocyanin 
that outwardly it appeared green these buds, even when sufficiently developed 
to show two divergent lobes representing the first leaf-pair, may nevertheless 
be coloured a \leep red in every cell, thus presenting a striking contrast 
with the axis on which they are borne. Here a general flooding of the 
whole embryonic structure has taken place under altered physiological 
conditions. In passing it may be nqted that the presence of adventitious 
buds on the hypocotyl has now to be viewed from the point of view of the 
development, normally and not as the result of mutilation or other injury, 
of a branch from foliar tissue, which furthermore shows no differentiation 
in the way of affording fixed points for their origin. For there seems no 
reason to doubt, especially in view of the uniform degree of hairiness 
displayed from the cotyledon node to the ‘collar’, that the cotyledon skin 
is coextensive here, as elsewhere, with the hypocotyl axis. What is the 
immediate cause of these outgrowths which have no definite relation to the 
general anatomical configuration — the entering trace joins on anywhere to 
the inner face of a secondary xylem bundle by curving to one side (see 
Fig. 29)— is not self-evident. Possibly a clue may be found in the relation 
between the amount of parenchymatous and vascular tissue present in the 
axis. In the diarch root of Antirrhinum the primary xylem is extremely 
scanty in amount, there being only two or three small vessels at each pole. 
Secondary thickening sets i'n so early that it is a matter of considerable 
difficulty to obtain a section of a root in which secondary increase has not 
yet begun. The secondary xylem forms a solid core and is considerable 
in amount in proportion to the bulk of the root. In the hypocotyl also 
there is proportionately little parenchyma (generally two layers or at most 
three besides the bundle sheath), so that it remains extremely slender in 
spite of its considerable length. It is conceivable that these adventitious 
buds result from some extreme condition (? of tension) set up in the 
hypocotyl, which, where a larger bulk of parenchymatous tissue is present 
which can act as an absorber, or where the cotyledons or epicotyl grows 
more rapidly, becomes distributed or adjusted without the production of 
adventitious outgrowths. 
Summary of Conclusions. 
1. The surface tissue of the Spermophyte shoot axis is of foliar origin, 
that is to say, the leaves are decurrent not only in those types in which 
