ioi8 



A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1005. — Allium cepa. Photographs of stomata 

 showing the cycle of opening and closing during 

 twenty-four hours; correlated with the variations 

 of light, temperature and humidity. Stomata 

 closed, or practically closed, all night and open all 

 day. 



Fig. 1006. — Solatium tuberosum. Photographs of 

 stomata, on upper and lower surfaces of the leaf 

 respectively, showing the cycle of opening and 

 closing during twenty-four hours ; correlated 

 with the variations of light, temperature and 

 humidity. 



{From Loftfield, Carnegie Institute Publication 314, by 

 permission of the Carnegie Institute of Washington.) 



