77 



nite age incline downward in spring when the temperature is lower and 

 straighten up later with increased warmth, that the creeping habit of growth 

 of Alpine plants may be ascribed in part or entirely to the influence of the 

 low temperature. A\'e can not agree with this theory. 



RosenthaP made investigations concerning the mode of growth 

 of trees in Alpine regions. He found that in all the species of wood studied 

 the annual ring is narrower in high countains than in the lowlands. The ec- 

 centricity of the branches is usually very great but the direction of the great- 

 est increase of growth varies. The vascular system, on account of the in- 

 creased evaporation, is more extensively developed. In dicotyledons, a 

 higher percentage of the vascular tissue is obtained by a narrower annual 

 ring; in conifers there is a considerable decrease of the late wood ring. 



The landslides which continually take place in mountains because of 

 storm conditions displace the trees and thereby change their woody develop- 

 ment. Hartig- pointed out the formation of broad annual rings and 

 so-called "red wood" (wood with short tracheids and strong lignification) 

 on the underside of the trunks and branches of the spruce as soon as they 

 bend toward the horizontal, while slender annual rings and "strain wood" 

 (long tracheids with weak lignification) are formed on the upper side. Ac- 

 cording to Giovanozzi^ this difference in the formation of the wood ring 

 of conifers is made use of in hygrometric measurements by the inhabi- 

 tants of the Piedmontese Alps since the small celled, thin-walled red wood 

 possesses hygroscopic characteristics very dift'erent from those of the strain 

 wood. The red wood side of a peeled branch becomes concave in dry air, 

 convex in moist air. 



According to the investigations of Cieslar* the lignin content of 

 spruce wood seems to be less near the upper boundaries of the tree zone than 

 in lower positions. 



It will be concluded from Cieslar's'' observations, that the suppressed 

 growth in Alpine forms is hereditary for the immediately following 

 generation, according to which spruces from seeds of trees grown in moun- 

 tainous regions grow more slowly when cultivated on the plains than do 

 plants raised from seeds of trees from the plains similarly grown. Engler has 

 made the same observation in seeding experiments at the forestry experimen- 

 tal station in Zurich. From germination experiments with the seeds of 

 spruce, pine and other forest trees, M. Kienitz*^ concludes that the minimum, 

 optimum and maximum germinating temperatures of spruce seed indigenous 

 to lower regions are higher than for seeds grown in higher positions. 



1 Rosenthal, M. Ueber die Au.sbildung der Jahresringe an der Grenze des Baum- 

 wuchses in den Alpen. Dissei-t. Berlin, ^it. Bot. Centralbl. 1904. No. 43. 



2 Hartig, R.. Holzuntersuchungen. Berlin. Springer 1901. 



a Giovanozzi, Sul movimento igroscopico dei rami delle Conifere. Malpighia 

 XV, cit. Bot. Jahresb. 1901. Sec. II, p. 191. 



4 Cieslar, A., Ueber den Ligningehalt einiger Nadelholzer. Mitt. a. d. Forstl. 

 Versuchswesen Oestei-reichs 1897. Part XXIII. 



5 Centralbl. f. d. gesamte Forstwesen, 1894. Vol. 20, p. 145. 



6 Kienitz, Vergleichende Keimversuche mit Waldbaumsamen aus klimatisch 

 verschieden gelegenen Orten Mitteleuropas, Ref. Bot. Zeit. 1S79. p. 597. 



