44 

 (46) With suitable objects, complete absence of pubescence may 

 even be obtained; for instance, in potato-rsprouts, in 

 Polygonmn amphibium. (according to Kerner) and others. 



The formation of roo* hairs, known to be especially- 

 sensitive objects, can also be easily arrested, or' entire- 

 ly suppressed. In many plants grown in water cultures, 

 the formation of root-hairs may be omitted. In other cases 

 we find it disappearing only in nutrient solutions of un- 

 suitable composition, Thus Schwarz found root hairs pro- 

 ducei in V7eak solutions O.E per cent of KNOg, but not in 

 strong ones, 1.5 per cent. The qualitative composition of 

 the nutrient solution is also of great signif icence, Trad- 

 esoantia roots remain incompletely pubescent in nutrient 

 media free from calcium, vifhile, in solutions containing 

 calcium, the hairs are numbrous and viell formed. 1 



The investigations of slimy epidermal cells does not 

 furnish anything essentially nev;, • They are lacking in the 

 aquatic form of Polygonum amphibiuy ,^. in specimens of Salix 

 retuga and Daphne striata, when cultivated in the moisl6 

 air.g Their development may be arrested also by fungus in- 

 fection, ^ as well as by the unknown factors causing the 

 variegation of leaves, ^ 



In the treatment of the mesophyll, however, we will 

 take no account of relatively rare cell forms, such as 

 crystal reservoirs, secreting glands, or stone -oells and 

 parts which store up v/ater, but will limit ourselves to 

 the mesophyll which has developed as assimilatory tissue. 

 As is v/ell known, a clearly recognizable differentiation in 

 the layers of the latter appears in the bilaterally construe- 



"1. Schwarz, Die Wurzelh. d, Pfl, T&binger Untersuch, Bd. 

 I, Pi 135 ,» Loew, Ueb, d, phusiol. Funktionen der Calcium- 

 und Magnesiumsalze im Pflanzenorganismus-, Flora, 189E, Bd. 

 LXXV, p, 368, According to Dassonville (Infl. des sels min- 

 eraux s, la forme et la structure des vegetaux. Rev. gen. de 

 Bot,, 1896, T. VIII., p, 284.) the formation of hairs is 

 omitted in distilled water. Compare with this also the state- 

 ments of Pathybridge, (loc. cit.) . If, according to these 

 statements, the formation of the root hairs can be suppressed 

 by exposure to light, we may see in this only an indirect 

 action of the light, which is made effective by fluctuations 

 in transpiration and turgor. CompEre here, also Reinhardt, 

 Plasmolytische Studien z. Kenntnis d. Wachstums d, Zellaeuv 

 bran. Festchr, f, Schwendener, 1898, p. 425. 



2, Volkens, Standtjrt und anat. Bau. Jahrb. Berl. Garten, 

 1885, Bd. Ill, p. 1, 



3. Lazniewski, Beitr. z. Biol., d. Alpenpfl. Slora, 1896, 

 Bd. LXXZII, p. 224. 



4. Negar, Beitr, z, Biol, d, E3?ysipheen. Flora, 1902, Bd. 

 XC, p. 221, 



5, Timpe, loc. cit. Beobachtungen an Crataegus monogyna 

 and Ulmus campestris . 



