182 
Journal of Agricultural Research 
Vol. VIII, No. s 
on the under surface, and the outgrowths are almost entirely from the 
loose parenchyma of the leaf (PI. 50, 52). In structure these tumors 
are either pure hypertrophies or mixed hyperplasia and hypertrophy 
(PL 50-54)- 
Also*, I obtained numerous fine intumescences on cauliflower leaves by 
exposing them for a short time to mixed vapors of ethyl alcohol and 
acetic acid (Carnoy’s fixing fluid), but only when the stomata were 
nearly closed (presumably). In maturer rapidly transpiring leaves on 
the same plant the effect of the vapor was entirely different—that is, 
there was a localized killing effect, giving to the leaves a curious mottled 
green-and-white appearance (Pl. 55). I looked in vain on such leaves 
for intumescences. There was not a trace even on the margins of the 
white spots. These leaves were in full growth and vigor, not old leaves. 
Those leaves which developed the intumescences were younger leaves, 
only partly developed at the time of exposure (PL 56). These would 
have their breathing pores closed or nearly closed at noon, and conse¬ 
quently only a stimulating minimum of the vapor could enter. The 
appearance of these growths in fresh vertical sections is shown on Plate 
57 and in cross and vertical sections from fixed and stained material 
on Plates 58 to 61. They are quite unlike most of the ammonia intu¬ 
mescences in structure, although derived in good part from the same 
tissues of the leaf (loose parenchyma)—that is, the ammonia intumes¬ 
cences, except two old ones, are made up almost exclusively of a few 
hypertrophied cells (Pl. 52-54), Miile these are composed of many inter¬ 
mingled small to moderately coarse cells, much more suggestive of a 
crowngall hyperplasia, than which, however, they are more regular. 
They also suggest incipient shoots—that is, growing points, and those 
7 days old show the beginnings of a vascular system derived from the 
smaller vascular bundles of the leaf (Pl. 60, 61). I believe they are 
actually* pathological growing points, and if so they are a striking ex¬ 
ample of the ability of the cauliflower leaf to develop totipotent tissues 
(embryomas) from many parts of its under surface when properly stim¬ 
ulated. The cells of these intumescences form a compact tissue that is 
very unlike the loose parenchyma from which it has been derived. 
There is, therefore, a suggestion in these results that one chemical sub¬ 
stance may induce hyperplasia of cells and another hypertrophy, both 
of which phenomena occur in crowngall and in various animal neoplasms. 
Still other substances are perhaps required to produce multinucleate 
cells. 1 
1 As distinguished from hyperplasia three striking instances of hypertrophy, of cells in connection with 
tumor growths may be referred to here: (i) The root nodule of legumes due to nitrogen-fixing bacteria, (2) 
the finger and toes of turnips and cabbages due to a spore-producing myxomycete, (3) galls on the roots of a 
great variety of plants caused by parasitic nematodes of the genus Heterodera. In the first and second 
cases the enormously enlarged cells are densely occupied by the parasites which destroy the cell contents, 
plasm and nucleus; and consequently these cells are not giant cells in the meaning of the animal patholo¬ 
gist, namely, not multinucleate cells. On the contrary, the enormously enlarged cells in the nematode 
galls should be of special interest to animal pathologists, because they are true giant cells, their development 
