NOTES ON RECENT RESEARCH. 



197 



Potato to respond to the application of manures in a degree quite 

 impossible to the Hough Giant " {I.e. p. 440). — E. N. 



Nutation of Pisum Stems. 



Nutation of Stems of Pisum (Bei. Bot. Cent. bd. 10, ht. 8, 



p. 128). — D. Neljubon has given an account of various experiments made 

 with a view to discovering the cause of the horizontal nutation recorded 

 under certain conditions for Pisum sativum. These experiments are fully 

 detailed, and the results are decidedly interesting. They show that coal 

 gas, and especially acetylene and methylene, in the air of a laboratory 

 produce a horizontal direction of the stems. This horizontal direction 

 was not produced when the laboratory air was artificially freed of impurity, 

 and appeared in seedlings grown in street air w^hen this had been artifi- 

 cially impregnated with small amounts of these substances. There are two 

 figures, and a full discussion both of these nutations and of the poisonous 

 eftects of small quantities of coal gas, SO2, benzol, &c. — G. F. S.-E. 



Parasitic Disease. 

 Parasitic Disease, Predisposition of Plants to. By Paul Sorauer. 



{Zeit. f. Pflanz. bd. x. ht. 6, p. 352; January 1901).— This was the 

 subject of an address by the veteran Prof. Sorauer, of Berlin, at a special 

 meeting of plant pathologists attending the International Agricultural 

 Congress at Paris last year. Case after case was quoted to show that 

 the presence of a parasitic fungus in any locality need not result in an 

 epidemic unless the plants acting as hosts are in a condition disposing 

 them to attack. We give as a summary of the lecture the resolution 

 passed by the meeting, which included most of the wwkers in diseases of 

 plants from every part of Europe : — 



" The methods in use at the present time for combating parasitic 

 diseases of plants ought to be amplified by a course of preventive treat- 

 ment for each species of cultivated plant. It is particularly advisable 

 to encourage research on the means of defence possessed by plants against 

 these diseases. The influence of soil, its improvement and manuring, 

 deserves the special attention of observers. The hygiene of plants is 

 indispensable, because experiments prove more and more that the propaga- 

 tion of disease depends not only on the presence of a parasite, but above 

 all on the constitution, the general health, and the predisposition of the 

 plant to attack. Efibrts ought, therefore, to be made to modify tliose 

 particular conditions of constitution and health which render the plant 

 susceptible to disease."— TF. G. S. 



Plurality of Pollen Grains. 

 On the Influence exercised by a Plurality of Pollen Grains 



upon the Off'spring'. By C. Correns (Bot. Cent. 1900, IS, 422 485).— 

 Experiments with Mimbil Is Jcdcipa and J/, long i flora demonstrated that the 

 best results as regards constitution of the offspring were obtained by a liberal 

 application of pollen grains as against a mere sufficiency. These species, 

 which have very large pollen grains and a single ovary, are peculiarly 



