J. SmolAk 139 



sections were made of some of the leaves ; others were cut with the 

 microtome. 



Fleming's strong solution, which is very satisfactory for cytological 

 work, was used as a fixing agent. In it the small pieces of the attacked 

 and healthy leaves were exhausted by the water-pump and afterwards 

 hardened in alcohol and embedded in paraffin. Many slides were 

 made from material of three different ages, i.e. the middle of July, 

 the end of September and the second half of October. By this means 

 I perceived that the observed abnormal structures to be described 

 later are not the consequences of autumn disorganisation; it can also 

 be shown that we are hot dealing here with artifacts. The sections 

 were stained by different methods but all gave the same results. Mann's 

 method (18, p. 735, Gram's iodine, eosin, toluidin blue), the inverse 

 method (18, p. 809) by mordanting with potassium antimony tartrate, 

 and the method of methyl-green with potassium hydroxide proved 

 the best. Also Heidenhain's hematoxylin, safranin with anilin water, 

 and gentian violet followed by eosin in clove oil were found satisfactory 

 for the work. 



The anatomical structure of the attacked leaves differs from that 

 of healthy ones. The thickness of the attacked leaves is somewhat 

 greater than that of the healthy leaves. The turgor of the tissues in 

 the former seems to be increased. GKissow (3, p. 393) states as the most 

 striking anatomical phenomenon exhibited by "silvered" leaves, "dass 

 sich die Zellen ausserst leicht von einander losen und in dem Wasser 

 des Praparates frei herumschwimmen. Nur mit ausserster Vorsicht 

 gelingt es, kleine intakte Sektionen zu erhalten." 



I also perceived that the cells of the spongy parenchyma fall apart 

 very easily so that it is very difficult sometimes to obtain the sections 

 intact. This happens only in the sections of fresh material, those cut 

 from the thoroughly fixed and carefully embedded material were quite 

 intact. And from such microtome sections the anatomical relations of 

 the infected leaves could be observed quite readily. 



The mesophyll of the leaves attacked by the Silver-leaf disease is 

 thicker than the mesophyll of the healthy leaves or of the healthy parts 

 of the attacked leaf. There are no striking changes in the length and 

 arrangement of the palisade cells. But we notice in the spongy paren- 

 chyma that some cells are stimulated to a more intense growth in length ; 

 the intercellular spaces are in this tissue greater than in the healthy 



