48 SCIENCE PROGRESS 



case of Malva rotundiflora, Convolvulus arvensis and C. sepium 

 the oldest leaves were most quickly attacked, but those of 

 Lepidium virginicum are equally susceptible whether young or 

 mature. Infection of the upper-leaf surface took place more 

 readily in Polygonum persicaria, Erigeron annuus and Lactuca 

 scariola, whilst Solanum carolinense was only infected from the 

 lower surface. 



Observations on the variations of spore-length of the same 

 species of fungus grown under different conditions gave strik- 

 ing results. Variation curves are furnished of the spore- 

 lengths of Septoria verbascicola grown on Agar and on Ver- 

 hascum blattaria. On moist Agar the range was from 30/* — • 

 90/A with the mode at 6i/a, whilst on dry Agar the mode was 

 54/1 and the range 32/A to 80/4. On the Mullein leaves the 

 difference between the spores on leaves in dry and damp con- 

 ditions was even more marked, the range in the former case 

 being 25/u. — 6$/t, and in the latter from 30/z. — 91/t. Growth on 

 a different host but with similar environmental conditions 

 caused practically no alteration in the spore dimensions. As 

 the author justly remarks, these results raise considerable 

 doubt as to the value of spore measurements for specific deter- 

 mination. 



PLANT PHYSIOLOGY. By Ingvar Jorgensen, Cand. Phil., D.I.C., 

 University College, London. (Plant Physiology Committee.) 



Plant physiological investigations present at this time a 

 rather interesting aspect. A general survey gives evidence of 

 a good many currents of thought, and although the resultant 

 at first sight might give rather the appearance of confusion, yet 

 it seems certain that we are at the beginning of a period of 

 progress in biological research. 



The realisation that the life phenomena of the plant are not 

 as simple as would appear at first sight, and that the plant ex- 

 perimenter could not control his material in the same rigid 

 way as the chemist and physicist, and that under " natural " 

 conditions only a very limited number of combinations of 

 external conditions is operative, gave rise to a transitional 

 period where different working hypotheses and guiding prin- 

 ciples were utilised in the collection of experimental data. On 

 the one hand we have the evolution of rather philosophical 

 conceptions and units, and on the other hand we have the 



