ZOOLOGY AND BOTANY, MICltOSOOPY, ETC. 533 



rendered necessary by difference of environment. The most common 

 modifications are : secondary out-growths from the walls of the guard- 

 cells, reaching their extreme development in the toothed guard-cells of 

 Nipa ; decrease in size of air-chambers and in the breadth of the 

 openings ; closing of the openings by cutinizing, over-arching or other 

 modifications of the neighbouring cells ; thyllosfe formations, stoppage of 

 the openings by wax, hairs, etc. These characters are combined with 

 each other in such a way that transpiration is most delicately regulated. 

 The simplest explanation of these modifications is to assume that all 

 members of the Palm family were originally capable of complete adapta- 

 tion to xerophytic conditions, and that the meso- and hygrophytic types 

 only represent extreme development in one direction, while that in other 

 directions has been suppressed. Thus the various adaptations are the 

 full development under favourable conditions of a capacity inherited 

 from the primary ancestors, and not new features induced by environ^ 

 ment. This theory is borne out by the fact that similar adaptations of 

 the stomata are found in groups of plants whose ancestry is probably 

 allied to that of the Palms. 



Anatomy of Pogonia. * — L. Moreau has studied the anatomical 

 characters of the five species of Pogonia, and finds that they resemble 

 one another in their mode of development and in the formation of the 

 tubercle from the outer cortex, and from conjunctive tissues of the 

 central cylinder of the stolon. They differ from one another in minor 

 details, such as the presence of hairs, etc., but most markedly in the 

 foliar ridges ; thus, in F. leguminosarum the lower surface bears ridges 

 which are narrowed towards the apex, while the upper surface has only 

 unicellular hairs. iVgain, in P. Renschiana, the ridges of the lower 

 surface are well developed, and not narrowed towards the apex, while on 

 the upper surface they are small and narrow ; in P. Thoucirsii the ridges 

 are inconspicuous on the lower surface, plate-like on the upper surface ; 

 in P. Sakose the ridges of the lower surface have broad bases and are 

 pointed above, but are entirely wanting on the upper surface. P. lanceolata 

 (the flowers of which are still unknown) has large pointed ridges with 

 narrow bases on the lower surface, and small, slightly pointed ridges on 

 the upper surface. 



Distinctions between the Wood of Populus and Salix.f^A. 



Burgerstein has studied the wood of the poplar and the willow in order 

 to find some means of distinguishing them one from another. The wood 

 of 66 species and hybrids of the willow and 11 species of poplar was 

 examined, and an exponent established in the following manner : — 

 Portions of wood having a thickness of a hundred to a hundred and 

 fifty cells were cut by means of a microtome and the medium height of 

 the cells was then calculated, while at the same time it was noted whether 

 or not these cells were pitted. The exponent was the quotient obtained 

 by dividing the median height of the pitted cells by the median height 

 of the unpitted cells. The exponent for the poplar always lies between 



* Rev. Gen. Bot., xxiv. (1912) pp. 97-112 (12 figs.). 

 t Bar. Deiitsch. Bot. Gesell., xxix. (1912) pp. 679-8i. 



