SIR J. LrPi^BOCK — rnTTOBIOLOGICAL OBSERYATIONS. 



387 



Fig. 119. 



Avhole seed, but arc ?.)ot divided. We must therefore seek some 

 other explanation, and I will suggest the following. 



In most of the species which I have examined, when the coty- 

 ledons remain in the seed they do not leave the ground. la 

 some cases, however, as in Anona (fig. 119), the caulicle is long, 

 stout, and rises in the form of a loop 

 during germination, Avhile the cotyle- 

 dons, which ^at first are very small, 

 gradually increase almost to the length 

 and breadth of the seed, tlirow them- 

 selves into undulations, and it being 

 perhaps on this account impossible to 

 withdraw themselves from the seed, 

 are eventually torn from the axis. In 

 Sjgnonia insignis^ again, the cotyle- 

 dons, though flat and leaflike, are un- 

 able to emerge from, or at any rate do 

 not emerge from, the seed. Tliis may 

 possibly give us a clue to such cases as 

 EsclischoJtzia and Schizopetalon^ wliich, 

 I would venture to suggest, may have 

 reference to the manner in which the 

 cotyledons free themselves from the 

 seed. If this is delayed, the young 

 phuit suflers considerably, and indeed 

 often perishes. That the process is 

 Dot, however, so simple as might be 

 imagined, may be seen from tlie inter- 



I , I 



estin*' case afibrded bv the Cucurbi- 



O 9/ 



taceje, where, in Mr. Darwin's words*, 



" the seed-coats are ruptured by a 



curious contrivance, described by M. 



Flahaut. A keel or peg is developed 



on one side of the summit of the radicle 



or base of the hypocotyl, and this holds 



down the lower half of the seed-coats 



(tite radicle being fixed into the ground), whilst the continued 



growth of the arched hypocotyl forces upwards the upper half, 



* ' Movements of Plants/ p. 102. In IVcIwitschia Bower has pointed out that 

 a corresponding process serves to absorb the perisperra, acting in fact as a 

 feeder to the young plant (Quart. Journ. Micr. Sci. vol. ixi.). 



Gernunating seedling of 



Anona. 



