the Embryos and Seedlings of the Cactaceae. 431 
they are forced apart until finally they stand out at right 
angles to the hypocotyl. Thus is germination completed. 
A distinct and important feature of this process is the 
remarkable and rapid swelling of the hypocotyl, and con- 
sequent immediate assumption of a succulent habit. On 
examination, however, I have found this to be due, not to 
increase in number of cells through division, but chiefly to the 
great increase in size of the cells already laid down. In an 
embryo of Cereus triangidaris , for example, lying in the seed, 
every cell is small and full of protoplasm and starch ; while 
in that which is fully germinated the cells are many times 
larger, each one is rounded, and has a thin film of protoplasm 
around the wall, whilst their number is very nearly the same 
in the two cases 1 . It is plain then that germination consists 
here simply of the absorption of large amounts of water, by 
which cells already laid down in the ungerminated embryo 
simply swell to full size, and no doubt with no material 
increase in dry weight. From this it follows also that up 
to the time when new substance is made by the chlorophyll 
in amount sufficient to enable new growth to begin, which 
period is roughly marked by the beginning of the growth 
of the epicotyl, there is no line to be drawn between embryo 
and seedling ; in other words, we may best speak of the stage 
where the embryo is still lying in the seed as that of the 
ungerminated embryo, and that in which it has come out, 
turned green, spread its cotyledons, but before it shows the 
epicotyl, as that of the germinated embryo. It is this marked 
and important stage of the germinated embryo, with the 
epicotyl just beginning to show, that I have tried to represent 
in the drawings which accompany this paper. The stages 
after the epicotyl is developed may best be called the seedling. 
The shape of the seed makes the young embryo asymmetrical, 
but as it swells it becomes more and more symmetrical in 
form, though it does not, as a rule, become perfectly so. 
There is naturally great variation in the rapidity of germina- 
1 The statistics upon this subject are to be given in a paper referred to on a 
later page. 
