829 



in planting freshly cut pieces, a decay easily occurs among them as soon as 

 even a little moisture is present in heavy soils. If on the contrary the cut 

 pieces are left a few days in the air, cork layers are formed under the cut 

 surface, which protect the pieces of tuber. If the tubers are cut too early 

 before sprouting, it may happen in some varieties that the pieces remain for 

 some time in the soil apparently unchanged without any sprouting of the 

 eyes. It is, therefore, advisable with tender varieties to spread the tubers 

 before planting in a light, warm, place until the eyes begin to enlarge and 

 then to undertake the cutting. 



The importance of the cork formation on the cut surface is shown by 

 an experiment made by AppeF, who supplemented the results of studies by 

 Kny^ and Olufsen^. While the two last named investigators perceived the 

 tuber's chief protection against infection by parasites to be the wound 

 periderm forming beneath the cut surface after a short time, Appel proves 

 that the potato is able to protect itself before the wound cork is produced. 

 He finds that in the most favorable cases the periderm formation sets in 

 only on the third day after the injury and ends after two days more. There- 

 fore, the wounded place would lie unprotected for that length of time 

 against the demonstrably rapidly penetrating bacteria of decay if the walls 

 of the undestroyed cells lying directly beneath the wound surface did not 

 turn to cork immediately on the side toward that surface. In fact, this cork 

 deposition completed after twelve hours was found in a part of the cell wall 

 of the first and second cell layers beneath the wound surface to be entirely 

 sufficient to prevent infection from Bacillus phytophthorus. The process 

 of suberization develops less well if the pieces of tuber dry at once and are 

 kept warm (for example, within doors). The outermost cell layers of the 

 cut surface then dry up so quickly that the two factors necessary for the 

 turning to cork, viz : oxygen and moisture, have only insufficient access to 

 the tissue layers under consideration. 



The closing of wounds in all fleshy parts of plants takes place in the 

 same, or a similar manner*. 



Grafting. 



Improving the stock by grafting consists in the artificial removal of one 

 or more buds and their insertion in a living part of a plant for the sake of 

 further nutrition and development. The inserted parts are usually held 

 fast by a bandage and protected by grafting wax from the injurious effects 

 of the atmospheric conditions. The inserted part can in general be called 

 the "scion," while the nourishing trunk is called the "stock." The newly 

 produced tissue furnished in part by the stock and in part by the scion. 



1 Appel, otto, Zur Kenntnis des Wundverschlusses bei den Kartoffeln. Ber. d. 

 Deutsch. Bot. Ges. 1906, p. 118. 



2 Kny, L.., tJber die Bildung des "Wundperiderms am Knollen in ihrer Abhan- 

 g-igkeit von ausseren Einfllissen. Ber. d. Deutsch. Bot. Ges. 1899, p. 1S4. 



3 Olufsen, Untersuchung-en iiber Wundperidermbildung- an Kartoffelknollen. 

 Bot. Centralbl. Supplement, Vol. XV, 1903, p. 269. 



* Kiister, Ernst, Patholog-ische Pflanzenanatomie. Jena 1903, G. Fisher, p. 1S5 ff. 



