4 
314 - BOTANICAL GAZETTE [APRIL 
Transpiration of evergreens.—PucGLisI"? has recently published a long and 
detailed paper on the comparative transpiration of evergreen dicotyledons in 
winter, spring, and summer. He discusses Laurus nobilis L., Laurus canariensis 
illd., Persea indica Spreng., Persea gratissima Gaertn., Oreodaphne californica 
Nees., Cinnamomum Camphora Nees. et Eberm., Litsea (Tetranthera) japonica 
preng. GARREAU’s method is used to determine the relative transpiration of 
the upper and the lower surface of the leaf, and the potometers of Morr and of 
PFEFFER for observations on detached shoots, sometimes continued for a week. 
The author’s most important conclusions are: that the volatile oils present 
are highly efficient in preventing excessive transpiration; that the safeguards 
against an injurious amount of transpiration in the leaves studied do not prevent 
rapid transpiration when there is an adequate water supply from the roots; that 
the relative transpiration rate of the upper and lower leaf surfaces varies decidedly 
at different seasons; that transpiration varies with the season, having a winter 
minimum, a maximum at the beginning of spring, and a lowering to or nearly 
to the winter rate during the extreme heat and drought of summer. 
The memoir is sufficiently important to merit attentive reading by everyone 
who is investigating similar problems. The results, however, should be scrutinized 
with care, since some of the values obtained by the potometer method are open 
to doubt. For example, in the losses per square decimeter of leaf surface obtained 
in the six sets of potometer measurements on transpiration of Cinnamomum 
Camphora, the values for the first day average nearly one and one-half times as 
large as those for the fourth day, of consecutive potometer readings for the same 
shoot. In the June readings for this species, the daily transpiration in grams pet 
square decimeter with the Mot potometer fell from 6%™ on the first day to 1. fi 
on the sixth day. Evidently some cause, perhaps the plugging of the vessels of 
the cut end of the shoot by bacteria, rendered the later observations valueless. 
The author cites some of the best literature on the subject, but apparently has 
not seen VON GUTTENBERG’s most important paper.**—JosEPH Y. BERGEN. 
Mistletoe as a pest.—Bray*? has investigated the so-called mistletoe pest of 
the southwest, especially its destructive work in central Texas. It seems that the 
mistletoe is most destructive in the region of transition from a humid forest climate 
to a dry climate less favorable for trees, for it is in such a region that the light 
becomes more favorable for the parasite. The destruction is due in part t 
mechanical injury, but more especially to the drain on the water and nutritive 
supplies of the host, which is effected by the “sinkers” connecting the parasite 
7 Puctist, M., Contribuzione allo studio della transpirazione nelle piante sempre 
verdi. Annali di Botanica 7:517-652. pl. 22. 1909. 
*8 GUTTENBERG, H. von, Anatomisch-physiologische Untersuchungen iitber das 
immergriine Laubblatt der Mediterranflora. Bot. Jahrb. 38:383-444. Pls. 7-9- i 
‘9 Bray, Witt1aM L., The mistletoe pest in the southwest. Bull. 166, Bur. Pl. 
Ind., U. S. Depart. Agric. pp. 39. pls. 2. figs. 7. 1910. 
