Floristik, Geographie, Systematik etc. — Pflanzenchemie. 61 



Wicken Fen near Cambridge, the Vegetation of which has beeri 

 described (Bot. Cent. 110 p. 29). The primary aim of the author's 

 researches is to throw light on the problem of swamp xerophytes, 

 and one aspect of the subject is dealt with in the present paper. In 

 considering the vertical distribution of the transpiring organs, the 

 various species are grouped into five ecological types, based 

 mainly on the relative positions of the larger leaves on the stem; 

 it is shown that the maximum leaf-size is attained at different 

 vertical levels. This difference of ecological habit results in a mar- 

 ked stratification of the Vegetation above ground, while subter- 

 ranean parts also exhibit stratification. After discussing evaporation 

 as a means of determining the extent to which the atmosphere 

 promotes transpiration, the author describes an evaporimeter, by 

 which evaporation and temperature readings were taken at different 

 levels in and above the Vegetation. He found that the air amongst 

 the Vegetation is more humid than that outside, and that the higher 

 and denser the Vegetation, the greater the differences in atmospheric 

 humidity between the upper and lower strata; the average evapo- 

 ration at three different levels in Vegetation 1-5 m. high was 

 A : B : C = 100 : 32-8 : 66; position A was above the Vegetation B near 

 the middle layer, and C near the ground. The temperature results 

 show that the highest layers are subject to a greater diurnal ränge 

 than either the free air above, or the lower layers of the Vegetation. 

 The transpiring organs in the lower strata are thus in more humid 

 air and under more uniform conditions than the higher layers of 

 the "general Vegetation level". The structure of the evaporimeter 

 used is described, and details of readings and manipulation aregiven. 

 The author also discusses the mutual protection afforded by the 

 massing of shoots at the same level, a characteristic feature of Fen 

 Vegetation, and shows that the physiognomy of the Vegetation, no 

 less than the structural modifications of transpiring organs, may 

 secure protection from excessive transpiration. It is also held that 

 few species in the Fen have to face precisely the same set of phy- 

 siological conditions: and that the arguments of authors who insist 

 that the so-called xerophytic structures of marsh plants can have no 

 reference to present-day conditions, are inconclusive. 



W. G. Smith. 



Pasquier, P. A. du, Beiträge zur Kenntnis des Thees. 

 (Diss. Zürich. 1908. 8°. VIII, 70 pp.) 



De cette longe etude sur les principes chimico-physiologiques 

 du the et sur quelques points de son anatomie, il laut relever les 

 principaux resultats suivants. 



Le siege de la cafeine dans la feuille est le mesophylle. II s'en 

 trouve de faibles quantites d"mrs~~la nervure mediane, dans les 

 rayons medullaires et dans le parenchyme du phloeme. L'epiderme 

 ne contient pas de cafeine. 



II n'est pas juste que le contenu des feuilles de th£ en cafeine 

 diminue avec la croissance. Bien mieux, il se produit une continuelle 

 augmentation de cafeine, toutefois cette augmentation va en di- 

 minuant. 



La cafeine et les alcaloides voisins doivent etre consideres dans 

 les vegetaux comme des excretas düs aux echanges de matiere; ils 

 ne rentrent pas dans la circulation. Ils se comportent comme la 

 purine des animaux. 



