June, 1915.] THE ORCHID REVIEW. 167 
by self-division, subsequently becoming developed into cells like those from 
which they were derived. These gemmules for the sake of distinctness. 
may be called cell-gemmules, or, as the cellular theory is not fully 
established, simply gemmules. They are supposed to be transmitted from 
the parents to the offspring, and are generally developed in the generation 
which immediately succeeds, but are often transmitted in a dormant state 
during many generations and are then developed. Then development is 
supposed to depend on their union with other partially developed cells or 
gemmules which precede them in the regular course of growth. F 
Gemmules are supposed to be thrown off by every cell or unit, not only 
during the adult state, but during all the stages of development. Lastly, I 
assume that the gemmules in their dormant state have a mutual affinity for 
each other, leading to their aggregation either into buds or into the sexual 
elements. Hence, speaking strictly, it is not the reproductive elements, 
nor the buds, which generate new organisms, but the cells themselves 
throughout the body. These assumptions constitute the provisional 
hypothesis which I have called Pangenesis.—Darwin, Animals and Plants: 
under Domestication, ll. p. 374- 
The collection of formative gemmules from every part of the organism 
to form a germ plasm was only put forward as a provisional hypothesis, 
and, although highly ingenious, was soon shown to be out of harmony 
with the behaviour of reproductive cells, the nucleus of which was shown to- 
be derived from the vegetative nucleus by a special process, to be presently 
described. At that time, however, so little was known about the organisa- 
tion of the reproductive cells that probably no other explanation was- 
possible,.and Darwin himself remarked: ‘‘ Pangenesis does not throw much 
light on hybridism, but agrees well with most of the ascertained facts.” 
It is now known that the nuclei of an organism all owe their origin to- 
the nucleus of a previous generation, and that nuclear development takes. 
place by a process of indirect division (called karyokinesis). This process, 
in its essential features, is alike in all the higher plants and animals, a fact 
which shows its antiquity. The nucleus of the vegetative cell consists of a 
fine network of fibres, and a definite number of bodies, called 
Chromosomes, which go through a series of complex changes, ultimately 
resulting in the transverse division of each chromoseme, after which the 
separated halves are drawn to the two ends of the original cell, this being 
followed by the production of a new cell wall. This continued division of 
the nucleus and the production of new cells is the basis of all vegetative 
growth. The process is somewhat complicated, but Strasberger remarks- 
that it seems necessary in order to effect an equal division of substance. 
between the two daughter nuclei. 
We now come to the development of the reproductive cells, the essentiab 
