EDGAR TULLIS 



/ 



pushings of two to four outer collenchyma layers, witli a tender, inner tissue. 

 The latter tissue was seen to be rich in chlorophyll and at times, in fact, 

 showed still definite chlorophyll grains. Similar disturbances could be 

 proved also in the midribs of leaves more greatly injured. 



Here the phenomena of browning were first perceived in the walls of 

 the ducts and then in the various peripheral groups of the bark. 



In wilting out of doors, due to frost, naturally such an increased supply 

 of water, as obtained here in the experiment by placing the cut leaves in 

 water, cannot take place and, on this account, the wilted organs retained 

 for some time, or permanently, the wilted condition, especially if a splitting 

 of the tissue and changes in the ducts reduced the conductivity. This can 

 take place differently not only in 

 the different varieties and individu- 

 als, but even in the different 

 branches of the same specimen. 

 An example of this was furnished 

 by an elm which stood in a pot 

 and in winter was brought into the 

 hothouse for forcing. The little 

 tree, which had been exposed to 

 a frosty night at only i degree C. 

 below zero, had developed t\\ o 

 forked apical branches which ap- 

 proximately corresponded to one 

 another in length, leaf number and 

 size. In this frosty night, however, 

 only scattered leaves of one shoot 

 had begun to wilt but did not 

 change color. The relaxed organs 

 did not recover after several days 

 retention in the warm, room but 

 showed no advance of the wilting. 



It is clear from this that zvilting due to frost is a very local phenomenon 

 not directly connected with the upward forcing of water by the root. 



In the phenomenon of the movement of twigs the different kinds of 

 movement may be easily explained if the structure of the individual branches 

 is more closely observed and it is seen how, in the maturing of the annual 

 rings, the thin-walled spring wood (Fig. ii8) constantly changes to a thick- 

 walled autumn wood with small lumina. In this connection the studies of 

 R. Hartig^ should be compared showing the change from thick-walled, red 

 wood to the light, porous strain wood within the same cross-section of a 

 spruce branch. In the adjoining Fig. 117 the red wood is found especially 

 strongly developed in the first annual periods on the upper side of the 

 branch. In later years these showed a sudden change, since rather the 



Fig-. 117. Cross-section through a spruce 

 branch. In the inner part of the wood 

 disc the solid red wood is shown on the 

 upper side of the branch but in the outer 

 annual rings it is seen on the under 

 side. (After R. Hratig.) 



Hartig, R., Holzunteisuchungen. Bei'lin, Springer, 1901, p. .50. 



