315 



gen and carbon-dioxid. With a gradual removal of oxygen, intramolecular 

 respiration is aroused only with a considerably lower percentage of oxygen, 

 than it is when the oxygen is suddenly decreased. 



The discovery that phenomena of suffocation occur also in seeds if their 

 tissue is entirely filled with water is of great value to the practical worker. 

 Usually when seeds are soaked they get the water necessary for germination 

 ^vithout having all the air pressed out of the intercellular spaces. If. how- 

 ever, the seeds are kept too long in water, decomposition sets in, in which 

 often a distinct ordor of butyric acid, a result of bacterial decay, becomes 

 very evident. In the same way experiments, like those of Just^, for example, 

 show that when air has been removed by a pump from the tissues ordinarily 

 containing air and the space filled with water, the percentage of germi- 

 ratio-'T is very greatly reduced. 



Wlien seeds have been put in layers on top of each other while damp, 

 it is not the excess of water, which so quickly destroys the germinating 

 power, but the excessive heating and formation of carbon-dioxid. Wiesner- 

 found also that the carbon-dioxid is developed later than the heat. Hence 

 its development is not the only source of heat ; this is to be sought also 

 in the absorption of water. The seed, coming in contact with water, con- 

 derses it as it enters the tissues and thereby frees heat. 



That an excess of oxygen is just as injurious as a lack of it, is natural. 

 Bert found that the oxidizing processes in plants are arrested by too high a 

 tension of the oxygen. A mimosa died at 6 atmospheres in common air, hav- 

 ing lost its irritability because of a lack of oxygen. If the air was made 

 richer in oxygen, a pressure of 2 atmospheres was sufficient to cause death. 



The Brusone Disease of Rice. 



The unusually dreaded brusone disease which manifests itself by the 

 appearance of rusty spots in the leaves together with a blackening and 

 drooping of the blades, has often been the subject of earnest study, ever 

 since Garovaglio in 1874 began investigating it. The majority of investi- 

 gators considered the phenomenon parasitic. Some thought it necessary to 

 assume bacteria to be its cause, and some held various fungi responsible, — 

 among others, Piricularia Oryzae Br. et Cav. 



Recently, however, Brizi' has made comparative cultural experiments 

 from which it becomes evident that an exclusion of air from the roots in 

 high temperatures in water cultures induces disease of the plants with the 

 phenomena of the Brusone disease. With these experimental results agree 

 very well the discoveries which have been made in Italy and Japan. It has 

 been especially observed that the Brusone disease usually appears if com- 

 pact, only slightly pervious soils are healed greatly and a rapid change of 

 temperature sets in. There then follows an affection of the root which 



1 Bot. Z. 1880, p. 143. 



2 I.andwi'-tsch. Versuchsstationen, 1872, No. 2, p. 133. 



■i Brizi, U., Ricerche sulla malatti del riso delta Brusone. Ann. Instituto agrar. 

 Ponti. 1905. Milano. Cit. Zeitschr, f. Pflanzenkrankh. 1906. 



