rn. iv] COBALT MKTlion. 105 



vantage of this I'n. -t, I.,, demonstrate a number of points in 

 the physiology of the stomata. The. sensitiveness of the 

 cobalt paper depends on I/he strength of the .solution 

 employed, for delieate reactions Sfahl recommends I p.e,. ; 



jnr I, he following we employ a 5 p.e. solution. 



Strips of cobalt paper are placed on each side of a 



hypostomaial leaf and aiv covered by glass plates which 

 should project beyond the edges of UK; paper. Stahl uses 

 in some ejises sheets of tale, as being less heavy and there- 

 fore more easily lixed in place than glass plates. The 

 glass or laic plates being gently clamped at the edges tin- 

 papers are confined in spaces in which the dry ness of the 

 ;iir will depend on the transpiration of the two surfaces of 

 the leaf. The paper on the lower surface reddens nipidly, 

 while thai on the upper side remains blue. 



A .simple plan is to lake :i pair of similar leaves, 

 placing ne, J, with the stomata upwards, the other, />', in 

 I IK reverse position on a dry folded cloth; after covering 



them \\ith a strip of cobalt paper, place :i, sheet of Ljlass 

 over them which makes a good conlact with the yielding 

 cloth. After observing the rapid reddening of the paper 

 over A, the experiment should be repeated, reversing tho 

 leaves, so that H has now its stomafa upwards. 



To demonstrate the small amount of transpiration 

 from the upper Mirlace of hypostomatal leaves \\ e make 

 use of Stall 1's method, \v/.. cementing to the leal surface 



the glass plates covering the cobalt papers. We use 



small glass plates about 2\ r ) em. X '.}'~> em. made by cutting 

 ordinary microscopic slides in half and attach them by 



1 Tim! is wil.li Ilir Hl,onml:i only mi tin- Imvn in f:icc ; Stnlil rocOITl- 

 mends 'I'ftiili .': i nt 1. 1 .ihiiihi, I'ynix foniiintnix, 1'n/uiliis iiii/i'it, Ac. 



