640 



soon, while still developing their vegetative organs. The leaf-body becomes 

 hard and the tuber-like swellings soon become woody. Annual seed-bear- 

 ing plants (grains and summer blossoms) ripen prematurely. Peas, sown 

 too late, succumb very early to rust (Uromyces). Kraus^ has already 

 advanced the theory that the turgidity of the tissue decreases with too high, 

 temperatures. 



Haberlandt, in his experimental plants, has found a splendid example 

 of the influence of drought in fungous attacks on plants. Of three pots 

 sown with wheat and left standing side by side during the whole period of 

 growth, the one where the plants were watered only enough to keep up 

 life, were so attacked by mildew (Erysiphe graminis) that the greater part, 

 at any rate, of the blame for the whole failure of the harvest must be 

 ascribed to the fungus. The pot, standing nearby and abundantly watered, 

 was' almost entirely shunned by the parasite-. Still more decisive is the case 

 which I observed with Podosphaera leucotricha Salm. Half of a number 

 of young apple trees in pots stood in a conservatory, the other half out of 

 doors back of this conservatory. All the specimens had retained through- 

 out the winter the oidia form from the previous year. The trees in the 

 conservatory exposed, without any protection, to the summer heat were 

 twisted out of the shape from the extensive spread of the mildew, which 

 developed to the perithecial fruiting stage. Those standing back of the 

 conservatories, in half shade and in moving air, lost the mildew. Hell- 

 riegel's^ experiments prove how much the production of plants suffers from 

 a wrong time of sowing, even without the action of parasitic enemies. 

 Barley sown in April, May, June, August and September in pots with the 

 same mixture of nutritive substances and soil moisture, under otherwise 

 entirely similar conditions, behaved absolutely diiiferently. That sown in 

 April developed very regularly grown, excellent plants, bearing ripe seeds 

 at the end of 88 days. The seed sown at the end of May grew into plants 

 which, at first, also developed very vigorously, but as a long period of heat 

 occurred toward the middle of July, at the time the heads push out from 

 the upper leaf sheath the stalk was retarded in its growth in length. Up to 

 the premature death of the plants (after yy days) the kernels had matured 

 only incompletely and remained flat ; they, therefore, had become ripe pre- 

 maturely. The latter sowings showed an increasing lengthening of the 

 period of growth (the September seed, for example, required 240 days) and 

 resulted in quite incompletely ripened grain. 



In regard to forest plantations, experience also shows that the losses 

 from transplanting of young forest trees vary according to the time it takes 

 place. Experiments in Mariabrunn* gave the smallest loss in spring trans- 

 planting. For spruce trees the number of dying examples of an April to 

 June planting increases only to decrease again in autumn transplanting 



1 Molekularkonstitution des Protoplasms. Flora 1S77, p. 534. 



2 Biedermann's Centralbl. 1875, II, p. 402. 



3 Grundlagen des Ackerbaues 1883, p. 352. 



4 Deutsche Forstzeitung- November 13, 1892. 



