1921] WELLS—ZOOCECIDIA f 373 
It would appear then, in zoocecidial ontogeny or zoocecidial 
evolution, that there occurs at first an overcoming or breaking 
down of the differentiation and morphogenetic mechanisms which 
bring about the normal expression of the host plant characters. 
When this has gone on to the point where no differentiation 
whatever ensues, the new advance is made in the direction of the 
prosoplasmas in which fundamentally new characters are caused 
to appear. Thus we have a remarkable turning point in gall 
evolution, namely, that at which the normal expression of the 
plant’s potentialities, locked up in its meristem, is inhibited. 
gall forms, from the most insignificant interference with normal 
differentiation te total suppression, are kataplasmas, and all those 
types arising as definite new structures from the final kataplasmic 
condition are prosoplasmas. 
As pointed out in connection with the recapitulation data, all 
prosoplasmas in their ontogeny pass through the kataplasmic stage, 
either in the actual reversion of partially differentiated tissue to 
the undifferentiated condition; or, if the cecidozoon is in contact 
with the meristem, there occurs the equivalent, namely, the com- 
plete suppression of the plant’s tissue characters, only the new 
ones of the prosoplasma appearing. 
For the sake of clarity the situation has been presented in 
Positive,. mutually exclusive terms. There exists, as would be 
expected, a small minority of galls which occupy the transition 
region between the kataplasmas and the prosoplasmas. In cer- 
tain of these, for example, prosoplasmic characters may exist 
along with kataplasmic ones. Such a gall is that of Phytophaga 
rigidae O.S. discussed by CosENS and Srncrarr (4), in which 
aeriferous tissue is found which they explain on the latent charac- 
ter hypothesis. According to this view the gall.is kataplasmic, 
but if we take into consideration the specialized structure, the 
“beak,’’ of the distal end of the gall (an ‘“‘umwallungen” develop- 
-ment), the form character of the scleridal and nutritive tissues 
(counterparts of which are not to be found in any normal part of 
the host or its relatives), we must conclude that this gall is also 
definitely prosoplasmic in nature. Thus in many forms both 
types of tissue characters may appear. It will be questioned at 
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