409 



h> 





sets in in the early spring when, as a rule, it is continued by a persistent 

 East wind, the opening of the buds, dependant on the alternating action of 

 sunshine and rain, will be delayed. The gummy masses 

 in the bud scales of many varieties of trees, usually due 

 to the gelatination of the tissue, must be softened by rain 

 to facilitate the development of the buds, while the resin- 

 ous and partially balsam-like products of this softening 

 in the scales, warmed by the sunshine, 

 give way at the same time to the pres- 

 sure of the buds. In continued dry and 

 windy, spring weather, the buds unfold 

 more slowly because the necessary 

 growth of the inner side of the scales 

 is prevented so that they cannot turn 

 back far enough. 



In the second kind of injury, the 

 young tip of the shoot, just appearing, 

 is suddenly exposed to the sharp rays 

 of the sun and to very great evapora- 

 tion in abnormally dry air, after the 

 protecting scale has been thrown ofif. 

 In order to understand this process, we 

 give a few illustrations from Griiss^. 



In Fig. 67 is shown the cross-section 

 through the bud covering of the oak ; 

 in Fig. 68, one through Pinus Mughus. 

 It is easy to distinguish the different 

 scales firmly overlapping above the 

 strongly developed epidermis of the 

 outer side and, by comparing the 

 two bud coverings, the increase of 

 precautionary protection in the conifers 

 is found to take place by means of the 

 deposition of masses of resin (h). In 

 the cross-section of the individual cov- 

 ering scales it is noticed that their outer 

 or, later, under side possesses especially 

 strongly developed elements. In the 

 pine, the epidermal cells have been very 

 greatly thickened sclerenchymatically. 

 The bud covering of the winter oak is 

 composed of 8 separate scales, and its cell layers found underneath the epi- 

 dermis are so strongly thickened that the lumina have almost disappeared. 



Pringsheims Jahrib. f. wissen- 



Si 



-ni-nr^/^-) 



Fig-.67. Cross-section Fig.GS. Cross-section 

 through the bud through the bud 



covering of Quer- covering of Pinus 

 cus sessili flora, Mughus, Scop. 



Sm. (After Gruss.) (After Gruss.) 



1 Griiss, J., 

 schaftliche Bot 



Beitrage zur Biologie der Knospe. 

 Vol. XXIII, Part 4, p. 637. 



