© 
MR. R. H. COMPTON : AN INVESTIGATION OF THE 
As we ascend the hypocotyl the xylem becomes reduced in bulk and breaks 
along the major and minor axes of the slightly elliptical stele, separating each 
protoxylem into halves: thus there are produced half-way up the hypocotyl 
four tangential bands of metaxylem with protoxylem on their eight margins 
(fig. 21). The phloem remains unchanged in position, so that but for tho 
position of the protoxylems the stele would eontain four typical collateral 
bundles, In the upper half of the hypocotyl the xylem is still further 
reduced in bulk and becomes more endarch, and towards the cotyledonary 
node a pair of ordinary collateral bundles is produced at each end of the 
ellipse (fig. 22). These pass out without further change to the cotyledons 
(fig. 23). No median protoxylem is present between the two bundles of the 
cotyledon trace in the mature state. 
ЕС-МІМОЅЕ Е. 
Mimosa PUDICA, Linn. 
A medium-sized shrub, with sensitive leaves *. The hypocotyl possesses at 
the base, just above the collet, a projecting rim or collar, which is 1:7 mm. in 
diameter. This is a point of agreement with the Acacieæ. The hypocotyl 
tapers slowly to the primary root. "The cotyledons are ovate, sagittate at the 
base, shortly stalked. De Candolle (1825, p. 19) gives a figure of the seedling. 
The root contains four narrow 1-2-seriate xylem plates, which meet in the 
entre of the stele. Тһе phloem is without fibres. А pith appears below the 
collet, and the four xylem plates are separated from one another; they 
gradually broaden internally, and at the external collet they assume 
the V-shape. Broadening of the xylem groups continues as we ascend the 
hypocotyl, and half-way up they are in the tangential position: the number 
of xylem elements is somewhat reduced during the transition, and the 
reticulate vessels are replaced by spiral. Fibres appear in the phloem in the 
lower part of the hypocotyl, but die away higher up. 
In the upper half of the hypocotyl- the polar groups of xylem decrease 
considerably in bulk, and each splits into two halves. The lateral groups 
also divide in half, but maintain their original strength. As the node is 
approached the stele becomes elliptical and the halves of the lateral xylems 
separate widely, making room for the appearance of the plumular traces. 
2 mm. below the node four bundles are found at each end of the ellipse : just 
above this they fuse in pairs, so that each cotyledon trace consists of two 
broad collateral bundles, which are now endarch. There is a short cotyle- 
donary tube, and small stipules are borne on the cotyledon petioles ; the 
cotyledons also bear the axillary buds. 
A zone of small-celled collenchyma is present in the cortex, as in 
Acacia spp. 
* The cotyledons are also sensitive, but on stimulation move upwards, whereas the. 
ordinary foliage leaves move downwards. 
