392 
Notes. 
nearer the central end of the cells. Very soon after flowering, 
thickening of the cell-walls of each of the three layers commences. 
The mode of thickening, which the cell-walls of the two inner layers 
exhibit, does not differ from that common to ordinary sclerenchy- 
matous tissues, and when completed the whole shows the usual 
stratification and pitted markings. The process is however a little 
more complicated in the outer layer, and recalls, in some degree, the 
manner in which the peristome of mosses is formed. Commencing at 
the central wall, the thickening deposit advances on the radial ones, 
but only extends to about four-fifths of the distance outwards towards 
the peripheral end of each cell, where it stops rather abruptly, and 
comparison of longitudinal and transverse sections shows that it is more 
strongly developed on the transverse than on the longitudinal walls. 
Bars and ridges of cellulose rise into the lumen of the cell both from 
the base, i.e. from the inner or central end of the cell, and also from 
numerous points on the radial walls. One result of the whole process 
is to drive the protoplasm, w r hich suffers considerable diminution in 
bulk during the process, outwards towards the peripheral end of the 
cell, the thickening substance being itself meanwhile converted into 
an almost solid mass of extreme hardness. Transverse sections 
taken at a somewhat later period show the endocarp, which is 
very hard and lignified, to be apparently enclosed in a sheath of 
tangentially flattened cells ( x , Fig. 23), an appearance which results 
from that peculiar absence of thickening in the peripheral regions of 
the cells of the third layer already referred to. It is not easy to 
arrive at a conclusion as to the use of such an unthickened portion, 
for it does not, as might be supposed, form a separation-limit, by 
which the stone is severed from the pulp when the fruit is ripe, but 
it becomes more and more indistinct as maturity is reached and is at 
length almost obliterated. 
Although the stony endocarp has been treated of as enclosing the 
seed as a whole, it is in reality discontinued at that place where the 
placenta is found; and the passage immediately above this, which 
served for the entrance of the pollen tube, is also never completely 
filled up. It is probable that this weak spot is of importance in 
allowing the growing radicle to push its way out of the shell, which 
it would certainly experience considerably difficulty in doing, were the 
covering continued evenly round the seed as a whole. 
J. BRETLAND FARMER, Oxford. 
