420 BOTANICAL GAZETTE : [DECEMBER 
The passage of radicles and lateral roots through potato 
Since Perrce found the penetration of living tissue by roots to be 
purely mechanical, I was not surprised at my failure to find sign of 
chemical activity on the part of penetrating roots in the tests above 
described. Prrrce, however, found the radicle of Pisum able to 
enter the unwounded potato, a result which was difficult to under- 
stand, as I was inclined to assume the hypocotyl of Vicia and Lupinus 
to be more delicate than the epidermis or periderm of potato. A 
repetition of PErRcE’s experiment gave negative results. I tried both 
old and new potatoes, and also fitted glass tube tips to the advancing 
root to reduce deviation of the tip, but in each test the result was 
negative. Since PErRcE used Pisum in his test, I tried that also, = 
addition to Lupinus and Vicia. If the periderm or epidermis 1s 
wounded, an easy entrance is effected by those radicles, and the root 
advances into the flesh of the potato. In tests with unwounded 
periderm there was always a deep impression of the potato. Micro- 
Scopic examination showed that the periderm cells were compressed 
and to some extent the hypodermal tissue also, but there was D0 
‘sign of corrosion. The advancing root formed callus, but when the 
periderm is wounded the callus does not form, and no evidence of 
obstructed passage is visible. 
For the sake of another method a potato was cut into halves ee 
the two halves tightly bound together with cord, so that the outside 0 
one half was in contact with the outside of the other half. Perfora- 
tions extending to within a few mm. of the periderm were made 1n 
one half, and into each perforation a seedling was inserted. ‘s 
whole preparation was then incased with gypsum. Thus each if i 
icle after penetrating a few mm. of the potato hypoderm found itse 
in contact with the inner side of the periderm. Further sae se 
brought the tip of the radicle against the periderm of the other h : 
of the potato from the outside. Strong impressions were made pose 
the periderm from outside. Microscopical examination eae” 
sign of any chemical activity. Since those same radicles goed 
traverse the flesh of the potato but do not enter the periderm 
the outside, one is almost forced to the conclusion that the mec sol 
push is too weak. The advancing root simply follows the eon 
least resistance as long as an advance or deviation is possiDi®- © 
