s8o 



the dying hack of the condnctinij curd (vascular bundle) ^vhich traversed 

 the healthy tissue and the tissue zchich became diseased. This, therefore, 

 could be the only after-efifect which can take place in frost injuries in case 

 there is no subsequent parasitic infection. 



In order to discoxer wliich 



might 1)0 the \ ery first effect of 

 frost on the tissue of the tree 

 and, therefore, which injury sets 

 in with the appearance of \er\- 

 lii^ht frosts, a whole course of 

 experiments was made on the 

 effect of slight degrees of cold, 

 but they did not lead to the de 

 sired results, lather no effect at 

 all was shown or the al)o\e-men- 

 tioned initial stages api)eared 

 simultaneously. The pruning was 

 extended further and further 

 back from the completely frozen 

 tissues into the healthy, basal i)art 

 of the twig and obser\ ations were 

 made to see which disturbance 

 had extended farthest from the 

 frost centre into the healthy tissue. 

 The frost action which could 

 be traced farthest into the 

 healthy zvood was found to be 

 the sivellinii of the intercellular 

 substances, i. e.. the middle la- 

 mella {V\g. I2() i). 



J found this striped swelling 

 and browning of the intercellular 

 substances to be in general more 

 frecjuent tangentially than in the 

 direction of the medullar rays, 

 esi)ecially often near the old 

 autumn wood, i. e., in the first vas- 

 cular layers of the si)ring wood. 

 But this condition of the inter- 

 cellular substances is rarel}" found by itself; it is usually associated with a 

 slight yellowish colormg and swelling of the secondary membranes of the 

 adjacent wood cells (Fig. 129 h). Tn some cases this change becomes so 

 extensive that the entire cell lumen is filled, excepting a narrow cavity (hh). 

 The power of refraction becomes extraordinarily weak with the swell- 

 ing, being retained only by the outermost manbrane and the firmer, inner 



Fig. 129. vSwel 



)f the ct 

 111 frost. 



