iqiq] currext literature 71 



in certain significant germinal factors. Thus if A is sterile with B and C, B 

 will be sterile with C. Shifting now* to the physiological technique, they 

 discover that sterility is tied up with the rate of pollen-tube growth. In cases 

 of selfing or cross-sterile pollinations, the pollen not only germinates success- 

 fully but develops a normal pollen tube. This tube grows through the style 

 at a uniform rate, but fails to reach its goal before the flower decays. In cases 

 of cross-fertility the poUen tube grows at a progressively increasing rate. 

 The logical conclusion is that self-sterility is not due to the presence of inhibit- 

 ing substances, but rather to the absence of accelerating substances (catalyzers 

 produced by the poUen-tube nucleus in compatible crosses, and only local in 

 their effect). At the wane of the flowering period self-sterility and cross- 

 sterility may be replaced by "pseudo-fertility." This is explained by the 

 breaking'down of the stylar tissue, so that own poUen tubes grow at a uniformly 

 greater (not accelerated) rate. — Merle C. Coulter. 



Photometry. — The probability that a solution of uranium acetate and 

 oxalic acid may be used successfully as a chemical photometer in physiological 

 researches involving the measurement and comparison of light intensities is 

 indicated by some experiments by Rldgway.' The solution used consisted 

 of I per cent uranium acetate and 5 per cent oxalic acid in aqueous solution 

 mixed in the proportion of 1:4. In various tests designed to compare the 

 oxahc-acid-uranium-salt photometer with the CaUendar pyrhehometer, the 

 chemical photometer gave results in general agreement with the pyrhehometer, 

 even though the 2 instruments involve different portions of the solar spectrum. 

 If the instrument and methods of using the solution can be reliably stand- 

 ardized, the inexpensiveness of the materials, ease of taking readings, accuracy 

 of determinations, and its automatic integration for variable conditions of 

 light during exposure w'ill make it an excellent instrument for extending our 

 knowledge of the influence of light as related to life processes in plants and 



animals. — C. A. Shull. 



1 



Nitrogen fixation. — ^Another contribution from the Missouri Botanical 

 Gardens on the subject of nitrogen fixation by lower organisms deals with 

 the growth of Azotohacter in synthetic media. Allen'" believes that most of 

 the discrepancies in the results of previous investigators can be explained on the 

 basis of the phosphorus requirements of the organism and the reaction of the 

 medium. He proves this in a fairly satisfactory way by means of the following 

 factors: (i) when CaCo3 is used to maintain a proper Ph in the media, the 



* East, E. M., and Park, J. B., Studies on self-sterile plants. II. Pollen-tube 

 growth. Genetics 3:353-366. ^g5. J. 1918. 



9 RtDGWAY, Charles S., A promising chemical photometer for plant physiological 

 research. Plant World 21:234-240. 1918. 



"> Allen, E. R., Some conditions affecting the growth and activities of Azotobacter 

 chroococcum. Ann. Mo. Bot. Gard. 6:1-44. ipiQ- 



