270 ON THE DEVELOPMENT OF VEGETABLE ORGANISATION. 
analogy is proved bv observation, in regard to the grains of feeula, 
which grow in the vegetable organs, till their forms and dimensions 
might render it difficult to recognise them. On the other hand, direct 
observation shows that, in consequence of this development, there are 
formed, in the interior of each grain of feeula, new feculent globules, 
which being packed together, present a very perfect resemblance to the 
cellular texture. Each of these grains of feeula, when obtained separate, 
is furnished with a hilum, by which it was connected with the inside 
of the cell which contained it, just as a bean is connected by its 
hilum with the placental parietes of the large ceil which we call the 
pod. But this bean is not merely stuck on to the surface of the pod ; it 
has been developed by the progressive swelling of the inside, and has 
passed successively through every dimension, from that of a microscopic 
globule to that which it possesses when ripe.” The secondary grains 
whose presence we have detected in its interior (that is, of the primary 
vesicles), acted on by the same causes, will be developed in their turn, 
and will in their turn give rise to other tertiary grains, and so on 
indefinitely : so that we shall then have a more or less complicated 
cellular texture in the interior of a single cell. Now as these new 
cells are, at every period of their growth, attached to the sides of the 
generating cell, we can conceive that each of them is nothing else than 
the development of one of the globules of which the coats of the cells 
are composed.”— Rasp. El. on Chem. 
It has been before observed that the development of the cells of 
plants is materially influenced by the varying circumstances of pressure 
under which it takes place. When the pressure is unequally distri¬ 
buted, being less in one direction and at the same time considerable 
in all others, the cells will be much modified in their shape. They 
will be compressed according to the direction in which the pressure is 
applied, and the active principle of growth continuing to be exerted 
chiefly in the direction of least pressure *, a series of elongated cells 
will be formed, approaching more or less to the form of tubes. To 
this modification of cellular structure, M. Link has given the name of 
elongated tissue. Sometimes the elongated cells, instead of being 
cylindrical, or prismatic, in their shape, are fusiform or spindle-shaped, 
that is, narrower at the extremities than in the middle. These are the 
clostres of M. Dutrochet. The medullary rays, or strice, found in the 
stems of dicotyledonous plants are also elongated cells, but placed in a 
* This is one reason, perhaps, why the vital membrane descends (as from the upper 
side of a wound on the stem of a tree) with more rapidity than it does from the sides or 
bottom—E d. 
