149 



secondary barl? end. from pith also produces elements of the 

 same kinid. The same differentiation is undergone "by the callus 

 of injured cotyledons (Vicia, etc.). of petioles (investigations 

 on Salix and Populus) and of roots (TaraxacuBil, 



Hext to the formation of tra-cheids, the development of an 

 epidermal tissue is the most Striking process of differentia- 

 tion in the callus. This too may he studied in the callus tis- 

 sue of poplar cuttings. Its outermost layers differ from the 

 inner ones first of all hy the greater volume of the single cells. 

 These are forced out into the form 6f pouches or long sacs. 

 Their walls, so far as they come in contact with the air, 'give 

 the reaction of me mhrtme* Cove rings which have become corK, 

 since they take up Sudan III-'' abundantly and at the s arte t'ime 

 are calored with phloroglucln and hydrochloric acid, like lig- 

 nified membranes, J do not doubt that the same substance for 

 a similar one) is the cause of these reftctions, just as occurs 

 fl66) in the "wound-gum" of very different plants , On closer obser*- 

 vation, delioate, pouoh-llke or serai -spheri can, convex |>roain- 

 enoes become noticeable on the outer walls of the calls, which 

 piay consist entirely of a gum-like mass, the reaction of which 

 we have Just mentioned, Mellinck has also observed these i» 

 callus formations on the petioles of Hymphaea**. An especially 

 good object for this investigation might be furnished by "Sie 

 "woolly s*ripes" of apples, which Sorauer* has described. The 

 woolly stripes are produced on the innerside of the core; def- 

 inite cell groups grow into thick little bunches of cell rows 

 lengthened to look like threads, (compare fig, 68), "which dif- 

 fer from those surrounding them in their thinner wall-f«rmati5an 

 and pass over very gradiially into the tissue of the fruit's 

 flesh". On these cells, wart-like dr knob-like "thickenings" 

 of the cell wall appear, as is shown greatly enlarged at the 

 left in figure ee''. The tissue described by Sorauer of which 



^ In using iSudan III, I generally proceed thus;- after 

 leaving the sections some minutes in a dilute solution of the 

 coloring matter, I then boll them in glycerine on the slide, - 

 During the boiling, the membranes which have become cork are 

 colored a strong red, 



^ Compare especially Prillieux, j:t, s. 1. formation de la 

 gomme A, 1. arbres fruit iers, Attn, Sc, Nat, Bot. 1875, 6°*^ ser., 

 T,l, p. 176. Frank, Ueb, die Guramlbildung im Holze u. deren Phys- 

 iol, Bedeut, Ber, d. D, Bot, Ges, 1884, Bd. II, p,321, Tarama, 

 Ueb, Schutz-u.Kemhglz,. seine Bildung u.s,physiol,Bedeutung. IiaAd 

 u.Kernholz d, laubbaume. Pringsheim's Jahrb. f, wiss. Bot, 1888, 

 Bd. XIX, p, 52. Molisch, Z, Kenntn, d. Thyllen etc. Sitzungsber. 

 Akad, Wiss. Wien, 1888, Bd. XCVII, Abt, 1, p. 264. Lopriore. 

 TJeber d^e Regeneration gespaltener Wurzeln. Nova Acta Leop,0ar61. 

 Acad, 1.896, Bd. LXVI, Kieler, Die gummosen Verstopfungen des 

 Zuckerrehrs. Beltr. wiss. Bot. 1898, Bd. II, p. 29 and many others. 



^ Zur Thyllenfrage. Bot. Ztg., 1886, Bd, X&fV, p. '5'45, 

 I think it more corj^ect to place the often multicellular forms 

 observed by Mellindk^ in wounded leaf stalks of Hymphaea among 

 callus forms, rather than, among tyloses. 



4 Handb, d. Pf lanzenkrankh. , 1886,2 Aufl., Bd. 1. p, 296. 



^ Apparently the same foiras can occur also in normal tis- 

 sue. Jost found them in the aerial roots of Phoenix spinosa . 

 (Beitr, z, Kenntn. d. Atmungsorgane d. ?fl, Bot. Ztg., 1887, Bd, 

 XLV, p. 601), Koack in the intercellular spaces in the roots of 

 various orchids (Ueb. Schleimranken in d. Wurzelintercell. ein- 

 iger Orchideen, Ber, d. D. Bot, Ges., 1892, Bd. X, p. 645). 



