Jan. 29, 1917 
Mechanism of Tumor Growth in Crowngall 
179 
separated from them by a wide tract of pith, while its phloem faces the 
pith cavity but does not come to its surface. Within itself the tissues of 
this abnormal xylem-phloem cylinder are arranged in a fairly orderly 
manner, but not as perfectly as in the normal outer xylem-phloem cyl¬ 
inder—that is, (1) there is an increased number of bundles, (2) the con¬ 
junctive tissue between the bundles is narrower and its component 
cells are smaller than in the normal xylem-phloem cylinder, (3) the cam¬ 
bium ring is thicker, (4) the xylem-phloem vessels are fewer, and (5) the 
wood fibers are more numerous. There are also many distortions strik¬ 
ingly suggestive of crowngall—that is, twisted bundles, spiral vessels, 
and tracheae lying diagonally or at right angles to the longer axis of the 
stem, and loops and distortions of the cambium (toward the pith cavity) 
leading in places to the formation of islands of xylem-phloem (well- 
staining tracheae and occasional sieve tubes) inside the second xylem- 
phloem cylinder close to the pith cavity (PI. 39-41), as if the plant when 
cut was in process of constructing other xylem-phloem cylinders more 
imperfect than the second because the stimulus was exhausted. The 
tissues in the imperfect third cylinder face the reverse way from those 
of the second cylinder, while those in the fourth face the same way. 
Beyond these is also a cambium without accompanying vessels (broken 
dark line, PI. 38, fig. 1). 
Great thickenings of the pith with the same cylindrical tearing loose 
of the inner (proliferated) part from the outer (normal) pith were also 
obtained with ammonia (PI. 29, fig. 1), with dibasic ammonium phos¬ 
phate (PI. 42) and with other substances, but no perfect double cylinder 
of xylem-phloem. I did obtain, however, in a young intemode next 
above an injected one (t^j- ammonia) a dislocation of a few vascular 
bundles extending the entire length of the intemode. These bundles are 
buried in normal looking pith (PI. 20) which forms a very decided ridge 
projecting into the pith cavity. Here the general appearance strongly 
suggests the pathological stele obtained in the tobacco stem, but the 
orientation of the xylem-phloem is exactly the reverse of that in the 
tobacco stele. In that there was an outer hollow cylinder of phloem, 
a middle hollow cylinder of cambium and an inner cylinder of xylem. 
In this Ricinus stele the outermost hollow cylinder is xylem, the middle 
hollow cylinder is cambium, and the central solid cylinder is phloem 
(PI. 43). If, however, we consider that part of each stele which faces 
the normal xylem-phloem cylinder they are alike—that is, they follow the 
general law of duplication of parts—viz, that the excessive part is a 
mirror image of the normal part. 
Moreover, the structure of these dislocated bundles is curiously like 
the whorls of tissue (tracheae, etc.) that occur in the tumor-strand or 
fundamental tissue in the interior of secondary crowngalls produced by 
Bact. tumefaciens. I have frequently figured (4, PI. 36, 39, 40, 83, 84; 
18, PI. 8, 12, fig. 48) and referred to these interesting whorls, but have 
