60 
WRIGHT : THE GENUS DIOSPYROS 
is laid down in the epicotyledonary leaves long before they 
are exposed to light. 
As to the causes which lead to the detachment of the 
cotyledons, it is very difficult to make any definite state¬ 
ments. The regularity of the occurrence in seeds of all 
sizes, under natural and artificial conditions, is suggestive of 
the possibility of a definite cellular activity cutting off the 
cotyledons at the node in a manner similar to that in which 
old leaves are cut off from the parent tree. This, however, 
cannot be the case, as in all experiments where the coty¬ 
ledons have been set free prior to detachment their dead and 
shrivelled tissues have persisted at the cotyledonary node 
for a considerable length of time. 
Hence we are driven to the conclusion that the detachment 
is probably a case of separation under conditions of strain, 
and several possible factors may be quoted in support of 
this contention. The first is the pressure of the endosperm. 
In those species where the cotyledons are persistent the 
endosperm may be equable (D. Ebenum) or strongly ruminate 
(D. sylvatica) ; similarly it may be markedly ruminate in 
species with detached cotyledons (D. hirsuta) or equable 
(D. insignis). Hence, the pressure of the endosperm, as 
indicated by the absence or presence of ruminations of this 
substance, has probably very little to do with the detach¬ 
ment of the cotyledons. A second factor is probably to be 
obtained in the bulk of the endosperm, testa, &c. ; for 
though D. ovalifolia may prove exceptional, it is a fact that 
those species with persistent cotyledons have relatively 
a smaller quantity of endosperm which is necessarily 
exhausted early, resulting in a shrinking of the testa and 
liberation of the cotyledons at an early date. 
However, neither of the foregoing, even if coupled with 
the increased resistance of the irregular surface of the 
mature cotyledons, can completely explain the cause of 
detachment. 
The chief cause, in my opinion, is to be found in the 
insufficient splitting of the testa ; in D. pruriens and D. 
