478 



BOTANICAL GAZETTE 



[DECEMBER 



the level of the water surface were taken as a basis for transpiring 

 surface, since these surfaces all contained stomata in greater or 

 lesser numbers. The unit of surface selected was, for convenience, 

 the square decimeter. 



Table VI shows the rate of transpiration in cc. per hour per 

 sq. dm. of total plant surface. Several things are brought out. 

 The rate during the day is usually much higher than the night rate. 

 This is not so apparent in the case of the water lily, for in this 

 instance the difference between day and night rates is not so great 

 as in the other cases. This is remarkable when it is considered 

 that the lilv leaves float on the surface of the water in a verv humid 



atmosph 



humid 



may 



for in part by the fact that the lily leaves, because of their contact 



warmer 



much cooler than the water during most 



nights. 



TABLE VI 



ARE 



/ 



Date 1910 



Conditions 



Aug. 10. 



10. 

 11. 

 11. 

 12. 



12. 



13. 



15- 



16. 

 16. 



17 



Day 



Day and night 

 Day 



Night 



Transpiration in cc. per hour per sq. dm. of total plant surface 



Pickerel- 

 weed 



Day 



Night 

 Day 



Night 

 Day 



Night 

 Day 



Day 



Night 

 Day 



1.758 

 0.274 



1.654 



1.603 

 o . 060 

 1.696 

 0.012 



Cat-tail 



1. 812 



0. 140 



1.665 



0.872 



0. 172 



1.670 



1-565 



0-332 

 1-483 



0.000 



1.608 

 0.054 



r-797 

 0.216 



2.129 



o. 108 



1-885 



Arrow- 

 head 



1. 194 

 O.146 



I.566 



O.718 

 O.224 

 0.501 

 O.044 

 O.827 

 O.056 



I 045 

 1.050 



O.OII 



0.920 



0.613 



o. 120 

 0.982 



Great 



bulrush 



2.463 

 O.616 



2-439 

 O.366 



^325 

 2.409 



3.690 



o-357 

 2.927 



0.244 

 2.409 



m 



I.789 



0-954 

 3.187 



Three- 

 square 

 rush 



Water lily 



2.007 

 O.627 

 0.750 



1. 481 



0.864 

 3.198 



2-439 



o. 122 



1.566 

 0.482 

 2.631 



Free 

 water 



. 





1.704 

 1. 184 



2.280 

 1. 125 



1.799 

 1.428 



2.017 

 o.8n 



2. 119 

 0.579 

 1.647 



1.083 

 0.605 



1.407 





1359 

 1.623 



2.281 



1.929 



i-95 2 



2.193 



1. 381 

 1.688 



1.820 



1. 118 



1. 118 



1.053 

 0.789 

 1.316 



Aside from these differences between day and night rates of 

 transpiration, there is also a great difference between the rates 

 from different species during the same time period. Again, the 



