the Embryos and Seedlings of the Cactaceae. 427 
an occasional mixing which happens through careless watering 
where several pots stand together ; the water carrying seeds 
may splash from one pot into another. It is not impossible 
that some of the remarkable cases of seeming polymorphism 
in seedlings described by Pfeiffer and others may be due 
to a mixing of distinct kinds ; and a wrong identification 
of a given seedling might thus readily come about. In 
obtaining the seeds I have tried especially to secure repre- 
sentatives of all the genera, of each of the marked divisions 
of a large genus, and of the morphologically remarkable 
species. Of the fresh seeds sent me by botanists there is 
hardly a case where they failed to germinate, though those 
which were bought often failed to come up. My experience 
is in marked contrast to that of .Henslow, who comments 
upon the great difficulty of germinating seeds of desert-plants \ 
After the embryos are well developed, however, it becomes 
increasingly difficult to grow them, though naturally there 
are the greatest differences between them in this respect. 
The transition from embryo to seedling, i. e. the formation 
of the epicotyl, is a crucial point which some cannot pass. 
They are very liable to rot at the root, or else to form there 
much corky tissue, which interferes with their proper nutrition 
and ultimately distorts and destroys them. Still with reason- 
able care, it is not difficult to raise most of the species. 
A very important question here arises as to how far the 
seedlings raised in a northern greenhouse correspond to those 
growing naturally at home, and whether safe conclusions as 
to the latter may be drawn from the former. At least one 
author (Schumann) has stated that the seedlings vary too 
much under these conditions to be trusted. But within 
certain limits I believe there is but little difference be- 
tween the domestic and the wild seedlings. First ; upon 
a priori grounds we might suppose that in one generation, 
while there may be changes in those characters, such as 
length, thickness, colour, which are developed in irritable 
Journ. Linn. Soc. xxx. 222. 
