1S6 



cross-walls is displaced more and more until it finally can , 

 occur at right angles to the normal direction. Schostakowitch 

 observed similar phenomena, He found that Dematiura pullulans 

 C6in be developed in the form of small tissue bodies By fUe'Tc- 

 /^»o\ *^°^ °^ ^ higher temperature. Figure 56 shows a thread of 

 (138) Hormidiura nitens of which cells have been irregularly divided 



under the influence of Congo Red^. Kny's^ investigations throw 

 light upon the influence of mechanical pressure and strain on 

 the direction of cell-walls, 



Miehe* observed cross-walls which are not formed at the 

 place where they would appear under normal conditions. AS has 

 been known since Strasburger, the mother-cells of the stomata 

 in the leaves of rfiny monocotyledons are produced on the apical 

 end of the .dividing epidermal cell. By different kinds of ex- 

 terimep tal interference Miehe has succeeded in reversing thTs 

 "polarixy* in such a way that the mother cells of the stomata 

 are cut off on the basal end. Klebs (loc, cit) observed un- 

 equal oell-division in Oedogonium etc. 



A, homOoplastic tissue 



We will terra homooplftsia each abnormal tissue formation, 

 which is produced by an increase of the normal elements. It 

 should be noted here, th&t "homooplasia", in. our sense of the 

 word, is not present in ever"^ increase of the normal elements 

 nor in every abnormal increase in volume of any organ v/hatever. 

 Through the cutting back of growing shoots, it is possible in 

 many plants to produce especially large leaves on the stump of 

 the shoot. Luxuriant nutrition leads often to the same result, 

 as demonstrated by the side leaves of many root sprouts which 

 have developed similarly to foliage leaves. Further, side 1 

 leaves may be brought to abnormally luxurient development by 

 the Removal of the foliage leaves which belong there, as showm 

 by Gobel. Now, since abnormally large leaves of this kind are 

 composed of cells approxitaataly as large as those in the small 

 normal ones, the large organs must without question be produced 

 by an overproduction of normal cells. It is clear, however, 

 that abnormal formations of this kind can not be the object of 

 our anatomical consideration, since, in the cases cited and in 

 analogous ones, anatomical variations from the normal are not 

 necessarily connected with the increase in volume. The abnor- 

 malljf large leaf shows the same anatomical structure as does the 



^ Ueb. d, Beding. d, Zonidienbildung bei Russtaupilzen. 

 Flora, 1895, Bd. 81, p. 376. 



Klebs, Beding. d, Fortpfl. bei einigen Algenpilzen, Jena 

 1896, p. 338. Congo red often exerts an arresting influence on 

 the longitudinal growth of the membrane. Klebs therefore as- 

 siimes that the cells treated with coloring matter only swell 

 out like balls, but cannot be elongated, "the further result of 

 this spherical form is, that, in the capacity for division, at 

 fifst not arrested, new walls are laid on to the old cell wall, 

 according to the principle of the least possible surface, and 

 divide the content of the ball, independent of the longitudinal 

 direction of the thread". For oblique division in Oedogonium 

 compare the s^e author » loc, cit. i;^^ 888. 



^ Kny, Ueb, d. Einfl. v. Druck u. 2ug auf d. Richtung der 

 Soheidewand in sich teilenden Pflanzenzellen. Pringsheim's 

 Jahrb. f. wiss. Bot., 1901, Bd, XXXVII, p. 55, Further litera- 

 ture references there, 



4 Ueb. Wanderungen d, pflanzl, Zellkerns. Flora, 1901 

 Bd. LXJOVIII, p. 105. 



