72 
Notes . 
immediately external to the stereom-sheath — and therefore removed 
some ten or twelve layers from the epidermis. By its activity several 
layers of cork are formed and the cortex is thus cut off from the other 
tissues, and during the second year is cast off in scales. It is 
this throwing off of the assimilating cortex in a plant in which the 
stem is the chief assimilatory part that presents such a curious 
analogy to the ordinary fall of the leaf in leaf-possessing plants. 
Just as in these, leaves of one year are functionally replaced in the 
succeeding year (in deciduous plants) by leaves borne on shoots of the 
same year’s development, so in such a plant as Rubus australis the 
assimilative tissue of one year, i.e. the cortex of the shoots of that year, 
is replaced in the next by the cortex of the shoots of the current year, 
and the last year’s cortex is cast off from the plant by the development 
of a periderm. 
Of course a similar state of things must occur, differing only in 
degree from this, in all cases in which a cork-cambium is formed 
inside any cortical layers, which assimilate even to a very small 
extent ; hence my comparison of this cortical shedding to leaf-fall may 
be considered a forced one. 
It seems to me, however, that such a contrast is justified — the agent 
in either case being the same, and the parts removed, though differing 
in morphological value, are physiologically identical. 
A good example of the same thing is found in Casuarina 1 . Here 
the stem-internodes have longitudinally-running ridges separated by 
deep grooves. These ridges are constituted almost entirely of 
radially elongated chlorophyll-containing cells. These form the 
chief assimilative tissue of the plant. Here also, as in the previously 
described case, there is a throwing off of this tissue. Periderm first 
makes its appearance in the grooves , and is formed here from the sub- 
dermal layer of cells. It is gradually continued across the tissue 
intervening between one groove and another, so that the ridges are 
completely cut off and by the second year begin to scale off. The 
resulting phellogen approximates in transverse section to a circle ; in 
the grooves the epidermis is the only primary tissue cut off by it, but 
between the grooves several layers of palisade-cells are removed in 
addition to the epidermis. 
F. W. OLIVER, Kew. 
1 Vide De bary, Comp. Anat., Eng. edit., p. 553. Also H. Ross, Berichte d. 
deut. bot. Ges., 1886, p. 367. 
