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IN VEGETABLE BIOLOQY. 535 



p 



and even with a 0-5-per-cent solution, to which tfessler's fluid 

 imparts a scarcely visible yellowing, the yellow colour is clearly 

 enough seen in many of the hairs and epidermal cells. Let us 

 now see how this operates in nature. A wet day comes, and the 

 leaves and stems of herbs, shrubs, and trees are flooded with 

 water containing ammonia in solution ; this must obviously cause 

 diffusion of epidermal and trichomal tannin in the form of the 

 yellow substance in question, and one can scarcely resist the 

 conclusion that the whole surface of the plant— at least in the 

 case of herbaceous plants— must play under these circumstances 

 an excretory role. And since dew contains a much higher pro- 

 portion of ammonia than does rain-water, the argument applies 

 with yet greater force to the nightly vicissitudes to which 

 vegetation is exposed. 



Hut the case becomes even stronger when we consider under- 

 ground parts. Among other ways in which ammonia is accumu- 

 lated in the soil, we know that decomposition of nitrates and of 

 nitrogenous organic bodies is ever going forward in consequence 

 w the activity of ammoniopoietic micro-organisms, and it can 

 scarcely be questioned that this soil-ammonia must be an efficient 

 agent in the excretion of tannin. 



obscure 



scare 









of them has made us much the wiser for his pains, though this is 

 scarcely a matter for special remark, in view of the abstruseness 

 oi the theme *. Some would have us believe that the tannins, 



tannin 



writer 



ccinctly 



within brackets :— Sachs ( ; Vorlesungen/ no. xi.) [Excretory and assimilative]. 

 Kutscher (< Flora/ 1883) [Excretory and assimilative]. Gardjner (Proc. Camb. 

 p hil. Soc. vol. iv. p. 388) [Excretory]. Vines (' Physiology of Plants/ p. 234) 

 [Decomposition-product, but indirectly assimilative]. Krays (F 



substance]. 



386) [Reserve 



3 rl. Akad. 1885 and 1887) [Assimilative]. 

 Belgique, 1886) [Assimilatire]. Dufour 

 rn. E. Micros. Soc. 1887) [Excretory]. 











Schulz (< Flora,' 1888) [Assimilative]. A. Fischer (Bot. Zeit 1888) [Assimilative]. 

 Hillhouee (' Midland Naturalist,' rols. 10 & 11) [Excretory]. Moeller (Ber. d. 

 deutech. hot, Gesell. 1888) [Assimilative]. Stahl (' Pflanam and Schnecken ' 

 w Jen. Zeitschr. f . Naturwiss. 1888) [Protective against animals]. G. Kraua 

 Gnindlinien zu «W Phv«iolo«e d. Gerbstoffi,' I*»P»& l889 5 ftbetr ' Iourn ' 









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Micros. Soc. 18fi{» rA„fi««ntin. excretory, and protective against animals]. 





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