1908] POND—LATERAL ROOTS 417 
cuticle if the latter is unwounded. When a root does enter, the 
passage is always around and not through the central cylinder, 
showing that the latter offers greater resistance than the cortex. 
Microscopic examination failed to reveal the slightest evidence of 
digestion of tissue. Many of the displaced cells of the cortex were 
found, but cells with broken walls were very scarce. The entering 
toot apparently presses the cortical cells until they collapse, and then 
laterally displaces them without breaking the walls. No trace of 
Corrosion of cell walls could be found. It seems probable that the 
mechanical push of the root is not sufficient to break through the 
cuticle when the latter is supported by underlying tissue. A demon- 
stration for this, however, is not claimed. 
Several tests were made to ascertain whether the central cylinder 
can be penetrated by another root at right angles. For this purpose 
€nough cortex was removed to expose the stele, and the glass root 
model held so that when withdrawn from the gypsum the canal led 
* directly to the central cylinder. In this way the entering root was 
compelled to enter the central cylinder at right angles or not at all. 
The result was negative in every case, and the entering root formed 
callus the same as in cases where the attempt was to enter the 
unwounded cuticle. The central cylinder was found to be strongly 
mpressed, but no sign of corrosion or digestion of tissue could be 
Observed. In some instances the entering root was able to shy 
from the stele and make passage through the cortex. Microscopic 
*xamination showed the cortex to contain compressed and collapsed 
cells. The appearance was the same as seen when the cortex is 
penetrated naturally by the lateral root. There was no evidence of 
“orrosion, the walls of the collapsed cells being just as thick and regu- 
lar in outline as those of the cortex in regions not affected by pressure. 
Longitudinal passage through the stele by main and lateral roots 
When the hypocotyl is traversed at right angles by another root, 
the tissue surrounding the path of the penetrating root cannot be 
“xamined microscopically with such advantage as is possible when 
the Penetrating root traverses the hypocotyl longitudinally for a 
“onsiderable distance. : 
The radicles of lupin seedlings having hypocotyls several centi- 
