488 
WALTER L. C. MUENSCHER 
the effect of leaf structure and of external factors on transpiration, 
and whether transpiration is a process of vital significance to the 
plant or whether it is a necessary evil to the plant. 
The work on the size and number of stomata for various species 
is rather limited but several rather extensive investigations have been 
conducted along this line of work. Several early investigators — 
Humboldt, 1786; Hedwig, 1793; Kieser, 18 15; Lindley, 1832; Krocker, 
1833; Meyer, 1837; linger, 1855; and Morren, i864' — determined 
stomatal values for a number of different species, the results of which 
are given in a summary table by Weiss (1865). 
Weiss in his very extensive work (13) gives the length, breadth, 
and area of stomata as well as the number of stomata per unit of area 
both on the upper and lower surface for 167 of the more common 
European plants. The results of these early investigators do not 
always agree and often their figures are very different. This may 
be explained as being due to the insufficient instruments for measuring, 
but more probably because different men used plants which were 
grown under different conditions or even used different varieties. 
Weiss observed that stomata may be present on underground 
stems and aerial stems as well as on leaves. He also states as a result 
of his observations that the presence of stomata is not limited by 
the surrounding medium; in other words, stomata may be present 
on parts of plants which are in air, water, or earth. 
Eckerson (5) determined the stomata-quantities for about 38 
common greenhouse plants. She gives a valuable table in which are 
recorded the length of the guard cells and of the pore of the stomata 
and the number of stomata per sq. mm. of upper and lower leaf 
surface for each species. 
The most important work on transpiration in relation to stomatal 
movement is by Lloyd (10). In his experiments on cuttings of 
Verbena ciliata and Fouquieria splendens he discovered that the 
rate of transpiration may undergo sudden and wide changes without 
any corresponding changes in the size of the stomatal aperture. 
From this he concludes that stomatal regulation does not occur, 
though, of course, conservation of contained water follows upon 
complete closure of the stomata; but it has not yet been proven that 
this ever occurs. 
The plan of my work was to determine the quantity of transpiration 
simultaneously for a number of species with various stomatal values 
