162 MR. P. GROOM—CONTRIBUTIONS TO THE 
spontaneous or whether it be the result of a stimulus conveyed by 
contact (compare the production of mechanical cells in elimbing 
organs). 
Structure of the Apex of the Root. 
A root-cap covers the tip. It is made up of comparatively 
few layers of cells, the outermost having thick cuticularized 
walls. Insome roots mucilaginous degeneration of large numbers 
of the meristematic cells of the root-cap sets in. The mucilage 
shows the same spongy structure and staining properties exhibited 
in the raphide-mucilage cells. The meristematic cells naturally 
are devoid of starch, but those immediately around the masses 
of mucilage are packed with starch. Travelling out from the 
mucilaginous mass, the amount of starch in the cells gradually 
diminishes till it occurs only on those halves of the cells which 
are nearer the mucilage, and beyond this point no starch occurs. 
Thus the process of degeneration into mucilage commences by a 
pathological accumulation of starch on one side of the cell; 
gradually this abnormal production of starch takes place 
throughout the whole cell, till it becomes packed with starch. 
My material did not permit me to trace the stages between this 
stage and the first one of mucilaginous degeneration of the cells. 
As might be anticipated in such massive succulent roots, it is 
impossible to see any sharp distinction into histogens. However, 
the very early differentiation of the exocortex is easily seen, 
as is the precocious development of the raphide-mucilage sacs. 
Recollecting that the piliferous layer of a monocotyledonous root 
is typically the external cortical layer, and that a multilamellar 
velamen is merely this layer divided by periclinal walls, it can 
be seen that the exocortex is genetically very similar to the 
velamen. Its origin, position, and contents would seem to 
indicate that the endocortex is, like the velamen, primarily a region 
of the cortex specially calculated to absorb and pass on absorbed 
liquids to the subjacent cells. And this hypothesis is further 
confirmed by the occurrence of a similar layer in rhizomes which 
perform the absorptive functions of roots. 
The roots of specimen B are much smaller and more slender 
than those of the larger specimen. Woodcut 1 represents the 
plant in its natural size. 
The distinction between the roots of the two plants merely 
consists in a difference in the number of cells. In addition, near 
