the Developement of the seminal Germ. 261 
able to induce germination in this manner, even after many trials. 
But according to the account of Du Hamel, the seeds of the mis- 
seltoe germinate by sending out a small and globular body at- 
tached to a pedicle, which, after it acquires a certain length, 
(about one-fourth of an inch I believe) bends ultimately towards 
the bark, into which it insinuates itself by means of a number of 
small fibres, which it now protrudes, and by which it abstracts 
from the supporting plant the nourishment necessary to its future 
developement. When the root has thus fixed itself in the bark, 
the stem of the parasite begins to ascend, at first simple and taper- 
ing, and of a pale green colour, but finally protruding a multipli- 
city of branches by continually dividing into jointed forks. 
If this description is correct, and coming from the pen of Du 
' Hamel I adopt it as the fact, it will be easy to show that the 
elongation of the radicle of the seed in question must necessarily 
be by ascent, because it is also a fact that almost all plants 
of the misseltoe originate in the lower surface of the bough on 
which they grow. Whatever, therefore, may have been the ori- 
ginal direction of the radicle, its ultimate direction must be that 
of ascent, before it can possibly reach the bark into which it is to 
fix itself. Now this is a case directly counter to the assumed 
principle of gravitation, which, till it is satisfactorily accounted 
for, cannot but be regarded as presenting an insuperable obstacle 
to the adoption of Mr. Knight s hypothesis. 
There is, however, a view of the subject which I have some- 
times regarded as giving even to the hypothesis of Mr. Knight a 
degree of plausibility worthy of some consideration. It appears - 
from the experiments of Du Hamel, which seem to have been 
repeated by Mr. Knight, that the radicle and plumelet do not 
augment their mass in the same manner. ‘The former elongates 
chief y by the apex, while the latter elongates by means of the 
2x2 intro- 
