162 STEWART: MUCILAGE FORMATION IN THE CACTI 
As noted, their cytoplasm is especially dense and their nuclei and 
nucleoles' proportionately large and very highly stainable, as shown 
in Fics. 2 and 3. Their growth is plainly a matter of the accu- 
mulation of largely increased amounts of protoplasm preparatory 
to their secretory activity in the production of mucilage. While 
there is plenty of evidence for believing that the cells increase in 
size during the period of mucilage production and possibly after 
they are completely filled, their increase in size before there is any 
evidence of the presence of mucilage in them is equally clear. 
A glance at Fic. 2 will show the number of cells which adjoined 
this large cell and will give some idea of how these hypertrophied 
cells, which are to form mucilage, compare in size with their 
neighbors. Fic, 1 shows one of the ordinary cells adjoining a 
mucilage cell. 
The mucilage or slime appears first as a very thin homogeneous 
film lying between the cell wall and the cytoplasm (Fic. 3). It 
stains but slightly and nowhere shows any conspicuous colloidal 
organization. In some of the older cells this layer persists about 
the periphery, while the remainder of the mucilage looks some- 
what fibrillar and is also vacuolated (Fic. 5); in other cells the 
strands and vacuoles extend almost to the cell wall (Fic. 4). 
As the amount of mucilage increases the cytoplasm is appar- 
ently crowded in toward the center of the cell, the nucleus and 
nucleole become smaller (Fic. 4), and while this is taking place 
both cytoplasm and nuclear-plasm become denser and lose their 
characteristically differentiated structure. Finally the nuclear 
membrane disappears and also the nucleole a8 such and the nuclear- 
plasm becomes merely a denser mass within the compressed and 
granular cytoplasm (Fic. 5). In the end nothing remains of the 
protoplasmic contents of the cell but an irregular highly stainable 
mass in about the middle of the cell. Sometimes this mass appears 
in section as a rather straight line, sometimes it has in section the 
shape of the letter Y. Many cells are also found which show no 
remnant whatever of the cytoplasm. 
In the cells-which are completely filled or nearly so, without 
exception the mucilage has the organization of a spongy substance 
full of vacuoles. Between and through these vacuoles there 
extend films, strands, or even threads, which radiate outward from 
