AND TRANSPIRATION OF TREES 1 19 



At eight o'clock the first weighings were made and tabulated. The 

 readings which were taken hourly, consisted of the weight of the bottle, 

 water, cork, and twig. At the end of the day the leaves were removed 

 from their twigs, placed in labelled envelopes, and dried in the warming 

 oven. 



Wl = weight of bottle, cork, water, twig, at 8 a. m. 



W2 = weight of bottle, cork, water, twig, at 9 a.m. 



W3 = weight of dried leaves. 



Wl-W2 = weight of water lost in transpiration between 8 and 9 a. m. 



Wl - W2 



X 100 = percentage of water lost in transpiration, based on 



"^^ dry leaf weight, between 8-9 a. m. 



Thus hourly water loss was calculated for beech, witchhazel, and 

 oak for each day's experiment. 



Because the experiments for water content and for transpiration 

 were made at the same time, no separate data for light and atmospheric 

 conditions were got for transpiration. Light intensity percentages 

 proved valueless for successive daily and seasonal work. Slight error 

 in transpiration rate might have crept in for the early hours of the day 

 when the leaves in the morning had been covered with dew. This 

 occurred only once, August 9, and then the dew was carefully absorbed 

 by blotters before the experiments were started. 



According to Haberlandt,^" and Klebahn," water is lost in transpira- 

 tion by the lenticels. The present method used did not take into 

 consideration the water transpired by stems. 



Selection of foliage of the beech was limited in the early summer 

 by. the presence of numerous egg-cases of some unknown insect. These 

 egg-cases were found on the ventral side only of the leaf. Oak galls, 

 on the oak leaves, were evident, but not numerous. On the witch- 

 hazel were many galls, containing nymphs of Hormaphis hamamelidis^^ 

 which were parasitic on the leaves. Within the galls were also unknown 

 larvae, which fed upon the nymphs, and later emerging, fed upon the 

 tissues of the leaf. As a result, the foliage of the witchhazel was greatly 

 damaged, and selection of leaves, in the late summer, was made most 

 difficult. 



^^ Haberlatidt, G. Beitrage zur Kenntnis der Lenticellen. (Sitzb. d. K. Akad. 

 der Wissensch. in Wien. Bd. LXXII, 1875, p. 175.) 



" Klebahn, tJber die Struktur und die Funktionen der Lenticellen, etc. (Ber. 

 d. Deutsch. Botan. Gesellsch. in Berlin, Bd. I, 1883, p. 113.) 



^^ Pergande, Theodore. Technical Series, Bulletin, number 9, U. S. Bureau of 

 Entomology — 1901. 



