339 



normal libriform fibres and an abundantly developed vascular system, the 

 wood of the diseased branch is made up almost exclusively of parenchy- 

 matous thin cells, between which the vascular cords are deposited. In 

 normal trees, under certain circumstances, the weakness of the wood ring 

 can be compensated for by schlerenchymatous elements in the bark^. 



The dropsical branches of pears differ from those of Ribes in that the 

 wood body is also involved in the parenchymatosis and entirely broken up. 

 By the rounding up and dilation of the wood cells, which have become par- 

 enchymatous, the ducts are gradually curved, displaced and finally torn. 

 Just as soon as the loosening process has affected the whole extent of a 

 fruit spear, or a "Fruchtuchen," dropping follows. 



The diseased branches came from trellised trees in a well watered 

 garden, richly fertilized with cow-manure. 



Even if such extreme cases are less frequent, yet the first stages, con- 

 sisting of the widening and excrescence of the medullary rays and the pro- 

 cesses of elongation in various groups of bark cells, are often observed. 



Swellings on the St. John's Bread Tree. 



Swellings often appear as a result of cell elongation and cell increase. 

 Savastano- reports thus, for example, of the outgrowths on the branches of 

 Ceratonia Siliqua. Conical outgrowths, rich in tannin, are found at the 

 tips of the flower stalks, causing atrophy of the blossoms. In an earlier 

 study^, he describes the production of larger swellings on the St. John's 

 Bread tree. On normally developed fruit branches, in the beginning of the 

 disease, the fruit falls in the first stages of development and the remaining 

 basal part of the axial cone begins to swell. The repetition of this process 

 in succeeding years produces a knotty swelling which can attain a very con- 

 siderable size and a height of 6 to lo cm. The bark of this hypertrophied 

 tip of the fruit twig is often seven times as thick as that on the normal 

 fruiting wood and the wood itself consists of ductless wood parenchyma. 

 In the almost pithy bark, the bast fibres have wider lumina and take an 

 unusual course. The medullary rays are twisted, the wood ring is often 

 bent. In the parenchyma, various cell groups with discolored walls and a 

 gummy content are recognizable. From the beginning of the disease, the 

 tannin content of the swelling increases, causing a distinct disturbance in 

 lignification. 



A case described by Vochting* in Kohlrabi plants may be mentioned 

 here. If all the vegetative points were removed, the leaf cushions swelled 

 to extensive structures. In the normal wood of the axis, as in the leaf 

 cushions, the cambium developed thin-walled xylem elements. In similar 



1 Pieters, A., The influence of fruit-bearing on the development of mechanical 

 tissues in some fruit trees. Ann. of Bot. Vol. 10. London, 1896. P. 511. 



2 Savastano, L,., Tumori nei coni gemmarii del carubo. Boll. d. Society d. 

 Naturalisti in Napoli. 1888. Vol. H, p. 247. 



3 Savastano, L.., Hypertrophie des cones k bourgeons (maladie de la loups) du 

 Caroubier. Compt. rend. 12. Janv. 1885. 



4 Vochting-, H., Zur experimentcllen Anatomie, cit. Bot. Jahresb. 1902. II, p. 300. 



