. Contributions from the Botanical Laboratory, vol. 11. Botany; Botany. Fig. 102.—The original experiment of Gurwitsch with onion roots. (After Gurwitsch.) point of attack by critics. Historically, it deserves mention, though later ex periments are more convincing and hiore readily duplicated. The first experi- ment which led directly to the discovery of Gurwitsch rays was done with the roots of onions. One root was held in a horizontal position close to and pointing directly toward another held in a vertical position (fig. 102). After some hours the tip of the vertical root, the so-called rec
. Contributions from the Botanical Laboratory, vol. 11. Botany; Botany. Fig. 102.—The original experiment of Gurwitsch with onion roots. (After Gurwitsch.) point of attack by critics. Historically, it deserves mention, though later ex periments are more convincing and hiore readily duplicated. The first experi- ment which led directly to the discovery of Gurwitsch rays was done with the roots of onions. One root was held in a horizontal position close to and pointing directly toward another held in a vertical position (fig. 102). After some hours the tip of the vertical root, the so-called receptor, was "fixed" (killed with chemicals), sectioned, and subjected to microscopic examination. It was found that in the receptor root there were more cells in the process of division on that side which had faced the sender than on the opposite side, indicating that the sender root had radiated some form of energy which accel- 412 My 'it 4^ ^k 4 ^ -t * ^ .4 crated cell division, or growth, in the receptor (fig. 103). The following table gives some results: Table 1 Mitotic cells Induced half of root Other half of root Difference in percentage Without intervening plate 292 770 464 2455 1422 231 634 312 2190 1200 +26 +21 +48 +12 +18 With quartz plate 934 476 733 395 +27 +20 In order to eliminate all effects possibly due to volatile oils given off by the onion which may have an influence on tissue, and further to ascertain the nature of the emanation, Gurwitsch placed glass and quartz plates between. direction of na 'f Fig. 103.—Section of a root tip which has been radiated, show- ing greater cell division on the treated (right hand) side. (From Reiter and Gabor.) the sender and the receptor roots. In the case of quartz, the increase in cell multiplication in the receptor still took place (see table 1). Ultra-violet rays pass through quartz but not through glass. For this reason Gurwitsch thought the "vital" rays comparable to, if not identical with, ultra-
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