338 



entirely removed. Maurer^ has recommended the use of Ribes nigrum in- 

 stead of R. aureum for budding stock. However, I have also known of 

 cases of excrescences on the axes of the black currant, especially after the 

 transplanting of such plants as tend to sterility. 



b). In Stone Fruits. 



It may be foreseen that, with the present methods of culture, phenom- 

 ena similar to those observed with Ribes, will also appear in other vari- 

 eties, for our fruit trees are becoming more and more delicate, due to the 

 great increase in nutrition supplied them. The mass of the parenchy- 

 matous branch substance increases constantly in comparison with the 

 prosenchymatous tissues. Between unbudded, wild stock, and budded 

 varieties there are considerable differences. Direct measurements have 

 shown me that the branches of the cultivated varieties acquire a fleshier 

 bark while the wood ring decreases considerably in thickness-. I have 

 called this increasing tendency of our fruit trees to form soft, parenchy- 

 matous tissues, storing up reserve substances, at the expense of the breadth 

 of the wood ring, " parenchymatosis." 



In special cases this change in development acquires such extreme pre- 

 ponderance that diseases arise. I observed such diseases especially in the 

 fruit wood of pears which is often shortened up to barrel-like fleshy swell- 

 ings; growers call these "Fruchtkuchen." The morbid disturbance con- 

 sists either in the shedding of the cork layers and outermost bark layers in 

 shield-shaped pieces from the side of the branch, thus showing a greenish 

 yellow callus-like tissue mass, or in the uplifting of the bark itself in stiff, 

 crumbly scales, like rings extending almost around the whole branch, with 

 similar changes in the tissues. In the latter case, all the branches found 

 above such a place are dead. 



If the diseased condition manifests itself in a less luxuriantly developed 

 fruit wood, which may be distinguished from the "Fruchtkuchen," as fruit 

 spears, a complete casting of these twigs was often found resembling that 

 of the normal dropping of the twigs observable every year in poplars. In 

 the present abnormal dropping in pears, the exposed surface was not smooth 

 but uneven and woolly, light colored, however, like the cross-section of 

 healthy wood. 



A cross-section through a place in the branch which is found in the 

 first stages of the disease, shows that the bark has developed strongly on 

 one side, especially within the primar}^ bark. Its parenchyma is thin-walled, 

 vesiculated in places or pouch-like and extremely porous. 



A comparison of the pith in a branch which has split and in a healthy one 

 '^f equal age shows that the former is one-third larger than the latter, while 

 the wood ring is only one-third as wide. Significant structural differences 

 are connected with these misproportions. While a healthy shoot shows 



1 Der Obstgarten, 1879, p. 182. 



2 Sorauer, P. Nachweis der Verweichliehung unserer Obstbaume 

 Kultur. Zeitschr. f. Pflanzenkrankh. 1892, p. 66, 



