212 



PHYSIOLOGY OF NUTRITIOX. 



parenchyma presents itself in transverse section as a tissue of only 

 slight thickness. It extends between the water-tissue of the 

 npper side of the leaf and a well-developed layer of parenchyma 

 on the under side of the leaf, whose cells certainly contain some 

 chlorophyll, but may likewise, from the quantity of sap which 

 they contain, be regarded as mainly of importance for the storage 

 of water. 



1 See Detmer, Journal f. Landwirthschaft, 1879, p. 119. 



2 See Just in Cohn's Beitrage zur Biolngie der Pftanzen, 1875, Heft 3. 



3 See G. Haberlandt, Phy siologische Pflanzenanatomie, 1884, p. 69. 



82. Further Experiments Respecting Transpiration. 



It is noteworthy that considerably less water evaporates in unit 



time from a given area of leaf 

 surface than from an equal area 

 this 



of water. To prove this I 

 made the following experi- 

 ment, using the apparatus 

 drawn in Fig. 79 : A glass 

 vessel, 11 cm. high and 8 cm. 

 wide, is filled with good garden 

 soil, in which a bean seed is 

 placed to germinate. When 

 the young plant has completely 

 unfolded its primordial leaves, 

 the vessel, whose rim has been 

 smeared with fat, is covered 

 with a glass plate divided into 

 halves and provided with three 

 holes. Through the middle 

 hole passes the stem of the 

 plant, packed, if necessary, 

 with cotton wool. One of the 

 two lateral holes receives a 

 thermometer, while the other 

 is fitted with a cork. We now 

 weigh the whole apparatus 

 described, and also a crystallising glass containing water. This last 

 in an experiment of mine was 5 cm. in diameter. After twenty- 

 four hours we again weigh the apparatus. The plant in my ex- 



FIG. 79. Apparatus for transpiration ex- 

 periments. 



