17-2 



very thick-walled, colorless epidermis (Fig. 20 e) lie three or four layers of 

 usually tangential ly elongated or cubical parenchyma cells (/>) which are 

 richer in cytoplasm than the deeper lying tissues and contain chlorophyll, 

 but no starch. The starch is found to appear gradually first in the inner 

 flesh and its grains usually increase in size toward the core. Underneath 

 the outer cell layers, rich in chlorophyll, the deposition of the stone cell 

 centres begins (st). These form groups of a few cells in the normal flesh; 

 in the coarse fleshed fruit they are separated only by small intermediary 

 areas of delicate parenchyma (^/'j. From the periphery toward the in- 

 terior of the fruit, the stone cell groups become more scarce and the sur- 

 rounding parenchyma assumes a stellate arrangement. 



In the first stages of the disease, we find in fruit, which is always green 

 and hard, that, underneath the uninjured and colorless epidermis, individual 

 cells contain no chloroplasts, but ha\ c a brown, strongly refractive cell con- 

 tent, which is massed together in lumps. The number of these browned 

 cells gradually increases and ruptures the outer skin. Beneath the ruptured 

 place which, by the dr}'ing and crumbling decomposition of the tissues forms 

 a depression (yr), a brown-walled dying tissue (br) is found in the 

 midst of the flesh, which later may rupture and form cracks. Often in 

 these cracks, and always in the open peripheral pits (gr), may be found a 

 colorless slender mycelium which is a subsequent infection and may hasten 

 the decomposition of the tissues. 



A most striking phenomenon is the fact that when the pit has been 

 formed the flesh tissues no longer die and closed masses of newly formed 

 schlerenchymatic tissue begin to push out like cushions with a radial struc- 

 ture (/). These cushions of stone cells force the dead bark (t) tissue out 

 and oflf. 



In cross-section the individual elements of the stone cell cushions are 

 square or rhomboid, and lie almost unbrokenly upon one another. Even in 



with nitric acid and washed with water, ammonia and alcohol this leaves behind 

 a yellowish white cellv^lose. Erdmann concludes from his investigations that the 

 substance of the stone cells may be produced from a carbohydrate by the loss of 

 water and nitrogen from starch or gum, while in the normal process of ripening, 

 water must be taken up for the formation of the sugar. 



The theory that the formation of sugar and of cellulose are most closely connected 

 is given expression by DeVries**. He says that usually an accumulation of grape 

 sugar is found in those young cells which later strongly thicken their walls. For 

 example, the bast fibres of clover as well as fibres of the inner fibrous sheath of the 

 vascular bundles, which appear to be very thick walled in a mature condition, are 

 rich in grape sugar in their younger, still thin walled stage, while the surrounding 

 tissue is poor in sugar or lacks it entirely. DeVries found the same conditions in 

 the young bast fibres of potato and maize. Even in the hairs, which are thick- 

 walled later, an accumulation of sugar takes place before the thickening of the 

 walls, thus, for example, in the hairs of young clover leaves, in who.se parenchyma, 

 however, no sugar could be proved. In the same way, according to DeVries, sugar 

 can not l>e found in the root parenchyma of this same plant, while in the young root 

 hairs it occurs abundantly. The possible transversion of cellulose to dextrin and 

 sugar by the action of dilute sulfuric acid after heating is well-known. With this 

 the recent investigations on the Hemicelluloses; mannen, galactan and araban, 

 should be compared. 



* Liebig's Annalen, Vol. 138, p. 101; cit. im Jahresbericht f. Agrikulturchemie 

 1866, p. 99. 



** Wachstumsgeschichte der Zuckerriibe, in den Landw. .Tahrb. 1879, p. 438. 



