THE VEGETABLE CELL. 
389 
process, as well as those already described, is relied on as 
demonstrating a point of cardinal importance in vegetable 
physiology, viz. that the vital portion of the cell is its proto- 
plasmic contents, independent of the cell-wall. 
4. Cell-division is the process which occurs in all repro- 
duction of cells connected with vegetative growth ; i.e., it is the 
sole means by which tissues are produced. The following 
modifications of the process are presented, viz. : — 
a. Where the whole of the protoplasm contained within the 
primordial utricle divides into derivative, or daughter-cells ; hut 
these daughter-cells do not secrete cell-walls until they have 
become completely isolated. This is the mode of formation of 
the zoospores of Achlyco and other less highly developed Algae, 
as well as the spores of Equisetum. If the whole protoplasmic 
body, in its contraction, were to form only one ball, the process 
would become one of renewal or rejuvenescence. Two varieties 
occur of this modification, according as the protoplasmic body 
contracts during its division, owing to the expulsion of water, 
or no contraction takes place. The pollen-grains of some En- 
dogens are formed on the latter principle. 
b. Where the daughter-cells formed by the division of the 
protoplasm of the mother-cell become coated with a cell-wall of 
cellulose while the division is taking place. This is again 
subject to two varieties, depending on the contraction or not 
of the protoplasmic body during division. The ordinary 
mode of the formation of the pollen of Exogens within 
the anther belongs to the first of these categories ; the second 
illustrates the mode in which ordinary cellular tissue is formed 
by the multiplication of cells. Fig. 6 represents this most 
common form of cell-division in the case of the filamentous 
Alga Spirogyra longata . The protoplasm-sac first begins to 
fold in at two opposite points, the line connecting which would 
often pass through the nucleus. The nucleus divides into two, 
the two halves gradually separating from one another and 
forming the distinct nuclei of the two new cells which are 
produced by the folding in of the protoplasm and the simul- 
taneous secretion from the protoplasm of a new dividing-wall 
of cellulose. 
Several apparently anomalous modes of the production of 
cells are known, to which special terms have sometimes been 
given; but they may all be referred to one or other of the 
modes now described. The formation of the 44 spores ” of the 
Mould-Fungi, and of the 44 basidiospores ” of the higher Fungi, is 
sometimes described as if it consisted in the 44 basidium ” or basal 
cell forming several spores in succession, which become detached 
one after another from the parent- cell. What really takes 
place is in all cases a bipartition of the cell of the hymenium, but 
