Anatomie. — Biologie. 533 



BOODLE, L. A., The Structure oft he Leaves of the 

 Bracken (Pteris aquilina Linn.) in relation to Envi- 

 ronment. (Journal of the Linnean Society, Bot. Vol. XXXV. 

 1904. No. 248. p. 659.) 



The leaves of the Bracken Fern growing in an exposecl 

 sunny habitat are shewn to differ from those of the same plant 

 growing in a shady sheltered locality in the following parti- 

 culars. In the first case the leaf is dwarfer and harder. The 

 thickness of the lamina and of the onter wall of the upper epi- 

 dermis is about twice as great as that in the sheltered form. 

 There is a well differentiated and almost continuous hypo- 

 derm, and a well-marked palisade tissue. The sheltered form, 

 on the other band, is softer, larger and more highly divided. 

 There is practically no hypoderm and the palisade tissue is 

 hardly differentiated. On the other hand, the spongy tissue is 

 more lacunar, and occupies a greater proportion of the meso- 

 phyll. 



The two types oi structure may occur in the different 

 pinnae of the same leaf. Thus in a leaf that had grown up 

 through a dense bush the pinnae immersed in the bush were 

 of the sheltered type while those that overtopped the bush were 

 of the exposed type. !t would appear, therefore, that the 

 mature type of structure is not determined at an early stage 

 in the growth of the leaf. 



A plant of an intermediate type was grown in a heated 

 and verv moist greenhouse, and it produced leaves of the 

 sheltered" type, although fully exposed to light. The fertile 

 leaves bore small sori with reduced indusia. The sarne plant 

 subsequently grown in the open air produced again leaves of 

 the exposed and intermediate types. Hence the amount of 

 illumination is probably not the only factor in determining the 

 structure of the leaf. D. J. Gwynne-Vauglum. 



HOLM, Theo., BiologicalNotes on CanadianSpecies o 

 Viola. (Ottawa Naturalist. XVII. 1903. p. 149—160. Plates 

 4-5.) 



Describes the cleistogamic flowers , Variation in foliage, 



structure of rhizome and rootshoots, as observed in Can a d i an 



violets. The following types of rhizome are mentioned as 



characteristic: 



A. Rhizome vertical, monopodial, leaves all basal with 

 axillary flowers (V. peclata). 



B. Rhizome horizontal, otherwise as in A (V. saggitata, 

 afflnls etc.) 



C. Rhizome horizontal or ascending, monopodial, with 

 basal leaves from the axils of which aerial stems develop with 

 leaves and flowers, but no stolons (V. pubescens, orbiculata). 



D. Rhizome a sympodial pseudorhizome with basal leaves 

 etc. as in C. (V. Canadensis, striata). 



