AGRICULTURAL BOTANY. 825 



moisture given off by pine seedlings at the age of one to three years and to 

 the influence of the weather on their evaporation. 



To determine the limits of the fluctuations In the amount of evaporation by 

 the seedlings in strict relation to age, in case of plants in vessels watered dally, 

 proved impossible since only year-old plants gave more or less homogeneous 

 magnitudes, while in the case of plants two and three years old the fluctua- 

 tions in the evaporation by individual pines were very considerable. The 

 evaporation considerably increases as the young needles attain normal dimen- 

 sions, but before the needles develop the evaporation Is feeble even at high 

 temperatures. The pines were found to evaporate in the spring considerably 

 less than in corresponding weather toward the end of the summer of the 

 preceding year, and this continues to be noticeable until the new young shoots 

 complete their development. 



In an experiment with gradually decreasing humidity of the soil, when the 

 pots were watered from two to five times during the summer it was found that 

 the seedlings which were watered and those which were not watered dried the 

 soil to a like degree nearly to the limit of minimum capacity for humidity; 

 also that the introduction of water into the soil caused a large rise in the 

 evaporation in young birches, while in pines the growth and evaporation were 

 affected only by the first watering in the beginning of the spring, watering In 

 the summer only slightly increasing the evaporation. The last mentioned fact is 

 explained by the development of the pine being completed by the middle of the 

 summer, in consequence whereof the water supplied later goes only to main- 

 tain the life activity of the developed needles. In young birches, on the other 

 hand, each watering induces the appearance of new leaves with a consequent 

 new Increase of evaporation. 



As to the influence of the weather on evaporation, the importance of the 

 temperature and solar radiation was accentuated. Observations on the course 

 of the daily evaporation in clear days showed the existence of two maxima, 

 the larger before midday and the other after midday. 



The effects of surface films on the rate of transpiration: Experiments 

 with potted potatoes, B. M. Duggar and J. S. Cooley {Ann. Missouri Bot. 

 Gard., l (1914), No. 3, pp. 351-356, pi. l).—ln a previous reijort (E. S. R., 30, 

 p. 726) the authors presented data concerning the application of a film of Bor- 

 deaux mixture to the leaves of castor bean and tomatoes. In the present pai)er 

 experiments have been extended to ix)tatoes to determine the effect of sprays 

 upon the transpiration of this plant. Potted potatoes in good growing condi- 

 tion were arranged in series of 10 plants each, the different series receiving 

 strong Bordeaux mixture, weak Bordeaux mixture, lime wash, lime-sulphur 

 solution, strong Bordeaux mixture and lampblack, and lime wash and lamp- 

 black. The water loss from the different plants was determined for 5-day 

 periods. 



The results obtained corroborated those previously announced, showing that 

 there was a marked acceleration of transpiration induced by spraying with 

 Bordeaux mixture, as also with some other films. The experiments not only 

 Indicate that Bordeaux mixture facilitates water loss, but that treatment with 

 a fairly thick lime wash or lime wash and lampblack also increases transpira- 

 tion. Lampblack added to Bordeaux mixture seemed to give a greater trans- 

 piration than Bordeaux mixture alone. This seems to indicate that the addi- 

 tional quality of color is a factor requiring investigation. The fact that injury 

 might result from the accelerated transpiration under the conditions of the 

 experiment does not indicate that a benefit might not accrue under field 

 conditions. 



