REACTION OF THE PLANT. gI 
shallow, no gall results. In the crown-galls, growth may begin, it would seem, in the inner 
wood, in the cambium ring, in the outer bark, or in the mesophyll of a leaf, 7. e., wherever 
cells are naturally dividing. The division of cells may take place so rapidly that all or a 
large part remain small. The earliest stages of the tumor formation have not been traced 
in serial sections. Soon more definite information will be available. 
In sections of young crown galls mounted unstained insterile water small clumps of bac- 
teria may sometimes be seen inside of unbroken cells and moving granules and rod-shaped 
bodies in small numbers some of 
which have appeared to be self- 
motile, the longer ones flexuous and 
occasionally one constricted in the 
middle, but stained slides have thus 
far given no clear-cut pictures. 
HYPERTROPHIES. 
In hypertrophied tissues the in- 
dividual cells are larger than normal. 
Usually both hyperplasia and hyper- 
trophy occur in the same growth, 
é. g., in olive-tubercle. Good ex- 
amples of hypertrophied cells occur 
alsoin root-nodules of Leguminosae. 
Here their volume may become 
many times that of the normal cell. 
Hunger pointed out that tyloses 
are very common in the vessels |. 
of plants attacked by Bact. solana- | — 
cearum, and ascribed their forma- 
tion to the presence of the bacteria. 
Of the correctness of this view I 
have since satisfied myself. The 
writer hasseen the same thing in the 
wood of young shoots of the mul- 
berry attacked by Bact. mori (fig. 
30). Here the stimulus to growth 
appears to be due to poisonous 
products absorbed by the vessels 
of the plant in advance of the move- 
ment of the bacteria. This is quite 
in accord with what we know 
of the action of many poisons, Fig. 27.* 
minute doses stimulating and larger 
doses destroying. The formation of tyloses in the manner described raises the question 
whether they may not be formed often under the stimulus of absorbed foreign substances, 
e. g., in the roots of old cucurbits where they are very abundant. Various attempts were 
made by the writer to stimulate their formation in roots of young cucurbits by addition of 
ammonia and ammonium acetate but thus far with inconclusive results. The tyloses 
sometimes appeared within a few days, but small numbers of bacteria also occurred and 
may have been the determining cause. Only when we are able to obtain them promptly 
without contaminating bacteria can we be certain. 
*Fic. 27.—Swelling on a potato shoot inoculated with a non-virulent culture of Bact. solanacearum (Va.). Plant 
118 inoculated Apr. 16, 1904. Photographed May 25. Disease at an end. 
