57 
Lee . — The Morphology of Leaf -fall. 
is present it is quite likely that the process of ligno-suberization will be 
complete, but if absent the cell-wall will but participate in the lignin 
produced in the surrounding cells ; and this accords with the facts observed. 
It is quite easy in some cases to demonstrate the inner film of suberin which 
may even extend round the exterior of the included crystal ; but in most 
cases no such film is to be observed. And the behaviour of the crystal 
cells when placed in the path of the developing scar cambium leads to the 
same conclusion ; for beyond the conversion of the cellulose wall into 
suberin with a little lignin there is no further change. If effective proto- 
plasm is present, why should not the crystal cell divide as do its neighbours ? 
But the crystal cell does not divide, and the chemical changes in its wall are 
probably the result of the activity of adjacent cells. 
Class I (b). Ribes sanguineum, Pursh. 
In the example about to be described it will be seen that the course ol 
events is not fundamentally different from that which characterizes Custanea 
sativa. The chief difference lies in the fact that here the process of ligno- 
suberization of the Protective-layer is usually fairly complete before leaf- fall. 
Other differences which have led to the erection of a distinct type by Tison 
are wholly due to the deep-seated nature of the stem-periderm, and are 
more apparent than real. 
In the mature leaf of Ribes sanguineum the upper, green, cylindrical 
portion of the petiole passes gradually into a sheathing base, the lower limit 
of which is marked externally by a slight furrow. The axillary bud is 
large, and its lower portion is completely hidden by the spreading base 
of the petiole. Both petiole and stem are covered with numerous hairs, 
which are often glandular and, as is well known, secrete the substance that 
gives to the plant its characteristic odour. 
The distribution of starch granules is rather peculiar, the places where 
these bodies are found being quite localized, and comprising the cork 
cambium, phellodcrm, wood parenchyma, and the periphery of the pith. 
At the time of leaf-fall starch granules are entirely absent from the primary 
cortex and the Separation-layer, two places where in other species they are 
almost invariably present. Compound crystals of calcium oxalate are 
numerous in both cortex and petiole. 
Apart from the occurrence of fibres in the vascular ring, stereome is 
entirely absent from the stem, so that here there is no question of the 
reduction of the strengthening tissue accompanying the vascular bundles as 
they enter the leaf. Just below each leaf three bundles leave the ring, and 
as they traverse the cortex and petiole they gradually converge, finally 
meeting in the upper part of the petiole and forming a large semicircle. 
Just above the leaf-base thick-walled sclerenchyma appears outside the 
phloem of each strand and later forms a continuous cylinder enclosing the 
