424 



tcctorum considcrahly enlarged in an absolutely moist room and became 

 markedly epinastic. The leaf rosettes were spread out because the inter- 

 nodes developed further. W. Wollny^ found that a lessened thorn de- 

 velopment occurs in normal leaves of Ulcx europacus as a result of con- 

 tinued atmospheric humidity. He also observed, however, that the chloro- 

 phyll content decreased as the leaves increased. According to Eberhardt-, 

 the number of chlorophyll grains is decreased if the stems become longer 

 and the leaves larger. In a later work' this investigator summarizes his 

 experiments as follows; moist air combines a reduction in the thickness 

 of leaves and stems with elongation. The formation of hairs is decreased, 

 that of blossoms and fruit retarded. l-Lpidermal, bark and pith cells become 

 longer, the intercellular spaces greater, the number of secretion canals 

 smaller and the development of the ^\•ood less noticeable. A smaller pro- 

 duction of lateral roots is noticed. 



E. Wollny'* also mentions that the time of blossoming and ripening is 

 retarded and, by numerous experiments, strengthens the easily foreseen 

 conclusion, viz., that the evaporation from plants and soil, under otherwise 

 equal circumstances, is smaller, the greater the atmospheric humidity. It 

 should be mentioned briefly in passing that in numerous cases abundant 

 excretion of water takes place in the form of drops with the reduction of 

 transpiration and by means of different devices in the various plants''. We 

 ffequently find this in potted plants which in the fall are brought into un- 

 lieated greenhouses, when the leaves touch the rapidly cooling window- 

 panes. 



Finally, I will mention the results of my own experiments". 



In trees (pear) the whole new growth and also the different individual 

 internodes and petioles were; observed to be shorter in dry air, and the leaf 

 blades more slender in moist air. In grains, the growth from seed was 

 found to be somewhat less in dry air; the leaf number was also somewhat 

 decreased, but the size of the individual leaves was increased longitudinally, 

 while somewhat lessened in width. The same change in dimensions was 

 also exhibited by the individual leaf cells. The influence of moist air 

 elongated the leaf sheaths and also the individual blades, as well as the 

 roots themselves, although the plants, even those exposed to dry air, stood 

 in a nutrient solution. 



The fact that the substance as well as the form of the j)lants will be 

 changed with varying humidity is to be surmised as a matter of course. 

 In fact, my experiments show that in moist air a lesser amount of green 



1 Wollny, W., Untersuchung-en iiber den Einfluss der Luftfeuehtiskeit auf das 

 Wachstum der Pflanzen. Inaugural-Dissertation. Halle 1898. 



i; E])ei-hardt, M., Action de I'air sec et de I'air humide sur les veg-etaux. Compt. 

 rend. 1900, t. 131, p. 114. 



3 cit. Centralbl. f. Agrik.-Chem. 1904, Part 8. 



4 Wollny, E., Untersuchungen iiber die Verdunstung und das Produktions- 

 vermugen der Kulturpflanzen bei veisohiedencm Feuchtigkeitsgehalt der Luft. 

 Forsch. auf d. Geb. d. Agrikulturphysik Vol. XX, 1898, I'art 5. 



■"' s. Hot. .lahresber. 25. Jahrg., Teil 1, p. 76. Abh. von Nestler und Goebel. 

 « Sorauer. Studien Uber Verdunstung. For.scli. aul d. del), d. Agrikulturphysik, 

 Vol. III. Part 4-5, p. 55 ff. 



