666 



peas and the kernels may be easily separated from the peas by sifting, while 

 the grain, generally grown with peas (summer rye and oats), is sifted out 

 with much more trouble and exhausts the soil more for the following winter 

 crop. 



Here also, as in grain, breeders are now directing their attention to 

 resistance to lodging. The Bulletins^ published by the German Agricul- 

 tural Society have proved to be most advantageous in this direction. They 

 contain the latest results of cultural experiments with the different varieties 

 of our cultivated plants. 



Lack of Light as Predisposition to Disease. 



When it conies to the attacks of jjarasites, the mechanical resistance of 

 the membranes of etiolated plants will be less. However, the atmospheric 

 influences become weaker and their fluctuations, reaching directly the cyto- 

 plasmatic cell body, can disturb its functions even if the etiolated plant 

 should work in the same way and with the same energy as one which has 

 sufficient light. 



The last is, however, by no means the case. 



The first indication of a change in function is found in the moving of 

 the chlorophyll grains toward the side walls, in the dark. At the same time 

 another significant change begins, viz., the closing of the stomata. Accord- 

 ing to Schwendener- this phenomenon, already observed in complete dark- 

 ness, also sets in with a sudden decrease in the intensity of illumination. It 

 is possibly not a result of the lowering of the temperature connected with 

 the decrease of light, for an increase in temperature within the usual fluc- 

 tuations causes no opening of this apparatus. Connected with this also is 

 the fact that a longer suppression, or reduction of the exchange of gases, 

 can bring about changes in the cell contents, due to a lack of oxygen, that is, 

 for example, a tendency to the formation of alcohol. These disturbances 

 will occur so much the more easily, the more intense the capacity for growth 

 and the greater the need for ventilation. Therefore, very young organs will 

 feel this, while old leaves, grown for many years, with a lesser need of light, 

 endure longer limitation in the exchange of gases. Nature indicates this 

 also by the wall thickening of the guard cells, increased with advancing age, 

 which, according to Schwendener, is so strong at times that no further 

 opening of the stomata can be possible. 



In regard to lessened transpiration, I found in young seedlings of 

 Phaseolus, dependent upon their cotyledons, such a difference between 

 etiolated and normal plants that the former, on an average, transpired in 

 the same period of time, 0.21 g. per sq. cm. leaf surface; the latter, 0.29 g.^ 

 The production of dry substance in a plant, under otherwise equal condi- 



1 Mittel. cler Saatzuchtstelle iiber wichtige Sortenversuche 1905-1907 usw. 



2 Schwendener, tjber Bau und Mechanik der Spaltiiffnungen. Monatsber. d. Kgl. 

 Akad. d. Wiss. zu Berlin, July, 1881; cit. Bot. Zeit. 1882, p. 234. 



3 Sorauer, Studien iiber Verdunstung. Aus WoUny's "Forschung-en auf dem 

 Gebiete der Agrikulturphysik." Vol. I, Part 4-5, p. 116. 



