166 THE ORCHID REVIEW. [JUNE, 1915. 
requiring it. Generally speaking, the species rest for a few weeks before 
emitting fresh roots, and should not be hurried or disturbed until then, but 
the hybrids, and especially those of complex parentage, often begin to push 
new roots even before the flowers expand, and therefore should be repotted 
as soon as the blossoms have faded. 
RIF 
bad THE MECHANISM OF HEREDITY. S| 
REAT issues, scientific and economic, centre round the mechanism of 
heredity, or why like produces like, and the explanations that have been 
put forward to explain why the various forces involved work out in the 
particular way they do are, as a correspondent very well puts it, both 
numerous and bewildering. The question is raised by a hybridist, and it 
takes the form as to the cause of partial reversion, or the transfer almost 
unaltered, after the lapse of a generation, of certain characters from a given 
parent to its hybrid offspring. Some phases of the question were discussed 
in our last volume, in connection with the remarkable amount of variation 
seen in Cattleya Sibyl (pp. 265-269, fig. 31), and we may now attempt t to 
carry the question a little further. 
In former days the belief was almost universal that species sepicdabd 
their own particular characters unaltered from generation to generation. It 
was regarded as a law of nature, like the law of gravitation, and this was 
probably the chief reason why hybridists and their productions were regarded 
with such particular aversion. It was thought to be sheer presumption to 
attempt to interfere with the laws of nature in such a way. This, however, 
is a digression. Even in those early days a few inquiring minds had begua 
to speculate. as to the way in which all the parts of an organism were 
reproduced with such marvellous fidelity, though nothing engaged much 
attention until the publication of Datwin’s Origin of Species, when that 
author wrote: ‘‘ The laws governing inheritance are for the most part 
unknown.” But Darwin had been meditating on the question, and some 
years later gave to the world his theory of Pangenesis, which we may give 
in his own words :— prs 
PANGENESIS.—It is a!most universally admitted that cells, or the units 
of the body, propagate themselves by cell-division or proliferation, retaining 
the same nature, and ultimately becoming converted into the various tissues 
and substances of the body. But besides this means of increase I assume 
that cells, before their conversion into completely passive or “ formed. 
material,” throw off minute gemmules or atoms, which circulate freely 
throughout the system, and when supplied with proper nutriment multiply 
