ZOOLOGY AND BOTANY, MIOEOSCOPY, ETC. 265 



adjoining epidermal cell by strands of cellulose, which afterwards become 

 cuticularized. 



In accordance with previous observations, he finds that, under normal 

 conditions, the stomata are always open in bright daylight, the opening 

 being effected by the turgidity of the guard-cells. It must not, however, 

 be assumed from this that the turgidity of the guard-cell decreases at 

 night, since in all the other cells it increases. In Potamogeton natans he 

 found the guard-cells always open at night under normal conditions, this 

 being the result solely of the turgid condition of the adjacent cells. The 

 stomata of native Orchidese and native LiliaceaB exhibit the peculiarity of 

 opening instead of closing in water, this resulting from the ordinary epi- 

 dermal cells losing their vitality much sooner than the guard-cells. In 

 these plants the stomata do not close at night. 



With regard to the closing of stomata at night. Dr. Leitgeb finds that, 

 in contrast to the large number of plants in which the stomata are closed 

 at night, there are certainly not fewer in which, under the same vital 

 conditions, they do not close. All plants do not show the same phenomena 

 when light is artificially shut out for a short time ; the stomata may either 

 close completely or not. Even in nature, however, plants belonging to 

 both these categories do not behave alike ; and in some the opening or 

 closing of the stomata in light or darkness can be brought about: at pleasure. 

 In all circumstances the stomata close as the result of too great dryness of 

 the soil, and commonly, even before the plant is observed to wither. In 

 some plants the stomata partially close in direct sunlight, even with an 

 abundant supply of water. In many, when the soil is sufficiently moist, 

 the condition of the stomata is determined by the degree of moisture of the 

 surrounding air, and is altogether independent of light. But all plants do 

 not behave alike in this respect ; an atmosphere saturated with moisture 

 is unfavourable in some, while it promotes in others the closing of the 

 stomata. It is therefore probable that the closing of the stomata at night 

 is, where it takes place, not an immediate result of the withdrawal of light, 

 which causes a decrease in the turgidity of the guard-cells ; but that it is 

 brought about by the lateral pressure of the epidermal cells against the 

 stoma, which pressure increases with the increasing turgidity of the plant 

 or of the organ which bears the stomata. 



Anatomy of Stipules.* — M. G. Colomb proposes to define the term 

 stipule more exactly than heretofore as any appendicular organ inserted on 

 the stem, the vascular system of which is formed exclusively of branches 

 of the foliar bundles before these have emerged from the cortex. He illus- 

 trates this definition in the cases of the hop, Viola tricolor and striata, 

 Galium, Huhia, the honeysuckle, Centranthus, Samhucus, and others. 



Peltate Hairs.t — Herr O. Bachmann has examined the structure of the 

 peltate hairs in a large number of species belonging to many different 

 orders. The commonest form, which he regards as the typical, is where 

 each cell has the form of a narrow wedge, all these wedges radiating from 

 the centre and united into a single plate, with or without a distinct stalk. 



This may be varied by the cells being conically elevated in the centre, 

 giving a cup-like form to the structure, or divided by cell-walls in different 

 directions, or by the centre being modified in various ways. Thus, instead 

 of being a point, it may be a line ; or it may be raised into a globular form. 

 The cells of which the peltate structure is composed may consist of two or 

 more layers ; or, on the other hand, it may be composed of two cells only. 



* Bull. Soc. Bot. Fiance, viii. (1886) pp. 288-94 (6 figs.). 

 t Flora, Ixix. (1886) pp. y87-400, 403-15, 428-48 (4 pis.). 

 1887, T 



