4E 

 toportant forms of upper-dermatogen cells, or rather of 

 thelx* derivatives come into question,- guard cells, hairs, 

 and slimy epidermal cells. 



An arrestment of the development of the guard cells 

 may be brought about in various plants by w611 knovm means. 

 Lowered transpiration and v/ak illumination cause a de- 

 crease of stomata. According to Stapf ' s count, in Solanum 

 t uberosum , there is , under normal conditions , one stoma 

 for every 46 epidermal cells. In the specimens vifcich he 

 let mature in gaslight, a pair of giiard cells occurred 

 for every S04 epidermal cells. The same reduction may 

 be proved for shade leaves, ^ 



(45) Contact with running vvrater acts just as does retention 

 in damp air, but often more energetically. According to 

 Mer, leaves floating below the surf act of the ?;ater do not 

 develop so many stomata as those which reach the surface. 

 In some plants, finally, the formation of stomata is omit- 

 ted entirely under the action of moisture. In many plants 

 which "normally" develop air and v/ater leaves, stomata are 

 found only on the former; in Stratiotes the submerged part 

 of the leaf is free from stomata, v/hile that above the 

 water possesses same. Stomata are entirely or almost en- 

 tirely lacking in leaves of Marsilia which develop under 



II 



1. Stapf , Beitr. zur Kenntnis d, Einfl. geanderter 

 Vegetationsbeding. auf die Formbildung der Pflanzenorg, 

 etc. Yerh. Zool. Bot. Ges., 1879, Bd, ZXVIII, p. 238. Prom 

 the further statements of Stapf, we gather that in the 

 "vapor- form" a stoma, occurred for every 50 epidermal cells, 

 in that cultivate in a room, only one for every 113* Re- 

 gular relations between the differentiation of the epider- 

 mis and the external factors may not be understood from 

 this; only so much is clear, that the number of the stomata 

 often decreases under abnormal cultural conditions. Dufour 

 made observations on shade leaves (Infl. de la lumiere s. 

 1, structure d. feuilles. Bull. Soc. Bot, Prance, 1886, 

 t, XXXIII, p. 92.) and Mar (Observe s. la repartition d. 

 stomates etc. Ibid. p. 121.) They proved that shade leaves 

 possess fewer stomata than sun leaves, Brenner fUnters an 

 eigenen Fettpfl. Flora, 1900, Bd. LXXXVII , p. 387) arrived 

 at the same results in the case of Mesembryanthemum, in that 

 when cultivated in a damp place, 19 to 23 stomata v/ere 

 found, instead of 50 to 52, as in a normal leaf. It is 

 very remarkable that in the case of other succulents under 

 similar cultural conditions, the number of the stomata in- 

 creases, fin Crassula 110 to 160 or 100 to 110, instead 

 of 90 or 70, as in the normal leaf.) Here also v/fere not 

 in a position to set up any rule. Compare also the results 

 of W. Wollny-, Unters. ub. d. Einfl. d, Luftfeuchtigkeit 

 auf das Wachstura der Pfl. (Diss.) , Forsch. Gebiet Agrikul- 

 tur-Physik, 1898, Bd. XX. Further literature is cited in 

 the following references. 



