850 



kinds of botanical nature curiosities. The one by Ludwig Klein^ may be 

 the most instructive at present. This seems especially fitted to arouse and 

 increase a love of trees by its more than 200 illustrations, made from photo- 

 graphic exposures. 



Wound Protection. 



^^'e have already partially discussed natural wound protection in so far 

 as it is produced by cork formation. In the wood body of trees, however, 

 no cork deposit is found rapidly covering the surface of the wound, but the 

 vessels in all such places are filled with tyloses or a gummy substance 

 (zvoiind gum) usually easily soluble in boiling nitric acid (dissolved with 

 difficulty in the Correae). This is found when healthy wood adjoins the 

 dead wood. As a rule, the tyloses are accompanied by some gum formation. 

 Both kinds of filling make the wood of the branch stump absolutely imper- 

 vious to water and air and quickly close the wound within the period of 

 growth. It is evident from this observation that we would do well to thin 

 our trees in winter shortly before cambial activity begins". 



In a great number of woody plants, the vessels and frequently many 

 of the other wood elements are filled with calcium carbonate''. This is 

 found, as a rule, in the heart wood and those tissues of which the cells have 

 a chemical and physical constitution resembling heart wood, such as the pith 

 enclosed by the heart wood and the dead, discolored wood of knots and 

 wounds. This filling is usually so complete that, after such pieces of wood 

 have been burned, solid calcium casts of the cells are found which had con- 

 tained the carbonate. The process may be explained as follows : whenever 

 opportunity is afforded, the soil water, containing the calcium in the form of 

 bi-carbonate, quickly passes through the wood cells and vessels, and gives 

 off carbon dioxid ; it also deposits the calcium, which is no longer soluble, 

 as a precipitate on the inner side of the vessels. In living heart wood which, 

 unlike the growing sapwood, cannot quickly work over the calcium salt, each 

 increase in temperature will cause the giving off of carbon dioxid and induce 

 the precipitation of calcium. In wounds, the carbon dioxid will likewise 

 disappear because of the exposure of the tissue. While the sapwood, which 

 deposits no lime, protects itself from the entrance of air by the formation of 

 tyloses or gum (probably as the result of the entrance of air into vessels 

 previously filled with sap) we find in heart wood a deposition of lime as a 

 means of protection. 



In the normal trunk, the formation of heart wood occurs first in the 

 advance stages ; after injury, however, it sets in at once and gives rise to the 



1 Klein, Ludwig, Bemerlvonswcrte Baiime im Grossherzogtum Baden. Heidel- 

 berg 1908. Winter's Univcrsitatsbuchhandlung-. 



2 Bohm, Uber die Funktion der veg-etabilischen Gefasse. Bot. Zeit. 1879, p. 229. 

 The most abundant literature on the formation of Tyloses may be found in Kiister, 

 E., Patholog-ische Pflanzenanatomie, 1903, p. 98. 



y Molisch, ijber die Ablagerung von kohlensaurem Kalk im Starame dicotyler 

 Holzgewachse. Sitzungsber. d. mathemat.-naturwissenschaftl. Klasse d. k. Akad. 

 d. Wissensch. zu Wien., Vol. LXXXIII, No. 13 (1881). 



