43 



water. ^ To this type belongs also, I suspect, the As- 

 plenium obtusifolu ia var. ^quatica . in v;hicli Biesenhagen^ 

 described the tissue differentiation as strongly reduced 

 and the stomata lacking; still others might be mentioned.^ 



Conditions for the formation of hairs are similar to 

 those for the formation of stomata. Because of the ease 

 of macrosoopic control the dependence of pubesence on 

 climate and culture conditions found early consideration.'^ 

 The trichomes are also arrested in development by the fac- 

 tors referred to. Etiolated plants, plants transpiring 

 poorly, or those vegetating under v;ater, develop only scanty 

 hair 'Coverin{g$^ 



1« Costantin, Etude, s. 1, feuilles s. pi, aqUatiques.Ann. 

 Sc. Sat, Bot, 1886., 7 ser,,T, III, p, 94, also Infl. du mil- 

 ieu aquati que s. l.stomates. Bull, Soc, Bot, Prance, 1885, 

 T, XXZII, p, 259. 'Schmidt E, , Einige Beob, z, Anat, d. Veg- 

 etationsorg, v. Polygonum, Diss, Bonn 187 9, Massart, L* ac- 

 commodation individualle chez Polygonum amphebium. Bull. Jard. 

 Bot. Bruxelles, 1902, Vol. I, fasc. 2, 



2, Ueber hygrophile Farne, Flora 1892, (Brganzungsband) 

 Bd, LXXVI, p. 157. Concerning leaves of the Twitches brooms 

 of ferns, compare belov;. Chapter V, B. 5. 



3. The question, v/hether the formation of the stomata may 

 be suppressed by unfavorable life conditions may have been 

 one of the first in the province of pathological plant ana- 

 tolay Tvhich v/ere taken up experimentally. In his "Anatome 

 der Pflanzen" (Berlin 1807) Hudolph refuted the statement 



of D.e Candolle (1801) according to whose explanation, "la 

 lumiere eSt encore necessaire au development des pores, Les 

 plants etiolees n^en ont aucun ." Rudolph found in etiolated 

 leaves of Ipomoea carnea and I. violacea stomata in normal 

 numbers, just as in the yotmg leaves of the bamboo, of calla 

 etc., which he had not exposed to light. In the case of the 

 variegated leaves of Arundo Donax, A, colorata. Agave amer- 

 icana . etc, (which Rudolph eIso reckoned among etiolated 

 ones) , equal numbers of pores v^ere found, according to him, 

 on the gree. and one the etiolated parts of the leaves, 

 Aga^n Rudolph refuted the further statement of De Candolle 

 (loc. cit) that land plants, grown under v/ater, can no long- 

 er form stomata. Experiments with Mentha prove the opposite. 

 "Any one who grows under water one of the plants designed to 

 grown on dry land, vn.ll not thereby take away its pores". 

 (Rudolph, loc. cit.) 



4, Compare thffise textbooks from the beginning of the 

 last century. One may here alsp be referred back to Goethe. 



5. Some citations of literature: Kraus, C, Beob.ub. 

 Haarbildung, sunachst an Kartoffeltrieben. Flora, 187 6, Bd. 

 LIX, p. 153; Kerner, Bflanzenleben, 1898, Bd. II, p. 449: 

 Costantin, loc. cit. Schober, Ueb. d, Wachst. d. Pflanzen- 

 haare an etiolierten Blatt-u.Achsenorganen.Zetschr. f. ges. 

 laturwiss,, 1886 ,Bd. L¥III,p. 586; Kraus , Aug. Beitr.z.Kenn- 

 d, Keimung. W. S. V/. unter Wasser. Mss. Kiel. 1901; W. Wol- 

 Iney, loc. cit. 



