874 



duced at first and gradually by further division the meristem of the young 

 sprout from which a roll differentiates as the first leaf. 



The roots are" formed laterally from a few cells lying near the cambial 

 zone of the vascular bundle. These, therefore, "endogenously" formed 

 roots soon rupture the overlying tissue. As l*"r. RegeP states, the roots of 

 begonia branch cuttings can aJso arise from the inter-fascicular cambium. 

 This author, who has investigated several other begonias beside Begonia 

 Rex with rhizome-like, recumbent petioles, as, for example, Begonia im- 

 perialis and B. xanthina, mentions that the formation of buds also takes 

 place on the leaf blade near the incisions. After the epidermal cells have 

 divided, the underlying collenchyma and the ground tissue are also drawn 

 into the new formation and help in producing the mound of cicatrization 

 tissue at the place cut. This tissue differs from that of branch cuttings 

 only in the fact that here the epidermis participates in the cell increase. 



This activity of the epidermis can become of very especial physiological 

 imi)ortance immediately after the cut is made since a few of the upper epi- 

 dermal cells near the wound elongate like hairs (pseudo-root hairs) and, 

 without doubt, develop a root-like activity until the true roots are formed. . 



In the adjoining Fig. 208 are shown the new structures on the cut sur- 

 face of a larger leaf rib in a hybrid Rex begonia. A indicates the old part 

 of the leaf, B the new structures. At first an abundant callus tissue {c) 

 develops from the cut and soon shows an apical growth of its cell rows but 

 indicates by the parallel edges of the cork cells that it is in the process of 

 transition to overgrowth edges. The endogenously formed new root (w) 

 breaks out on the under side of the boundary between the callus and the old 

 leaf tissue, while on the upper side, two new bud primordia have already 

 been formed. The younger one of these shows at d the meristematic tissue 

 of the young bud with the epidermis {e). This meristematic tissue is pro- 

 duced by the division of the original epidermal cells and the sub-epidermal 

 tissue. The second bud has been formed earlier at a point lying farther 

 away from the cut and already is further developed. The real bud cone {d) 

 is already overgrown by a more convex leaf primordium {hi) into which 

 extend young spiral vessels (/). The vascular bundle ring of the older 

 part of the leaf is indicated at g, while t indicates the vascular bundles 

 extending into the new root. 



Kny- noted that the vascular bundles had become larger on the petioles 

 of Begonia Rex, on which adventitious sprouts had been produced. The 

 cambium, like the adjacent ground tissue, had continued its cell division, 

 whereby the new walls between the adjacent bundles were predominantly 

 parallel to the outer surface of the petioles. Kny regarded this as the 



1 Reg-el. Fr., Die Vermehrunfr der Begoniaceen aus ihren Blattern usw. 

 Jena'ische Zeitschr. f. Naturwiss. 1876, p. 477; cit. Bot. Jahresber. 1876, p. 423, 439, 

 452, etc. 



2 Kny, L,., t)ber die Ein-schaltunj;: des Blattes in das Verzweig-ungssystem der 

 Pflanze. From "Naturw. Woclienschrift" 1904; cit. in Bot. Centralbl. (Lotsy) 1904, 

 No. 50, p. 612. 



