448 SUMMARY OF CURRENT RESEARCHES RELATING TO 



vascular bundles of prosenchymatous and parenchymatous cells. In 

 sonic Coniferre bordered pits occur in the parenchyma of the medullary 

 rays, which is never the case with Dicotyledons. The true vessels of 

 the Gnetaccaj are constant in all the threo genera. Ephedra, Gnetum, and 

 Welwitsehia ; the perforation of the wall is in the form of circular pores, 

 arranged in one or two rows; in Gnetum scalariform and elliptical 

 perforations also occur. 



In Monocotyledons wo find simple and scalariform perforations. In 

 Dicotyledons, simplo perforation preponderates greatly in comparison 

 with tho scalariform ; this latter is exclusively characteristic only of 

 somo small families, such as the Hamamelideae. 



Anatomy of the Leaf-stalk. * — Herr C. Plitt has examined tho 

 structure of tho leaf-stalk in 283 plants belonging to thirty different 

 families, with the view of establishing whether it can be used for 

 purposes of classification ; but the results are chiefly negative. 



Tho configuration of the vascular bundles of the petiole may be 

 either symmetrical or unsymmetrical ; and in the former case the 

 bundles form either a closed or an open system ; and of both these a 

 number of variations occur. In tho open system tho lino of symmetry 

 bisects the central bundle, which is often much larger than the others. 

 The closed system may exist either as a central ring of distinct bundles, 

 or as a central fibrovascular mass with compact xylem and closed 

 cambium-ring. 



The various types of petiole do not coincide with the various types 

 of stem. 



Permeability of the Epidermis of Leaves to Gases.f— M. L. Mangin, 

 as the result of a number of experiments, comes to the conclusion that — 



(1) The permeability of the epidermis of aerial leaves is very limited, 

 but is greater for plants with deciduous than with non-deciduous leaves. 



(2) When the surfaces are unlike, the permeability of the lower surface 

 of the leaf is greater than that of the upper ; it may be no more than 

 one-third more, but may be five times as much. 



(3) The permeability of the epidermis of submerged leaves without 

 stomata, is very great, and may be as much as twenty times that of the 

 most permeable aerial leaves. 



(4) Where the surfaces of the leaves are waxy, the permeability is 

 much diminished by the waxy material. 



Epidermal Reservoirs for Water.J — M. J. Vesque adds some fresh 

 ones to his previous observations on the adaptation of tbe epidermis for 

 the storing up of water. This was shown by the fact that when the 

 epidermal cells were placed in nitric acid not sufficiently concentrated 

 to produce plasmolysis (2-3 per cent.), or when exposed to excess of 

 transpiration over absorption of water, they decreased in volume. The 

 plants in which this was found to take place were Lilium candidum, 

 Tropseolum majus, Clematis Vitalba, Euonymus japonicus, Prunus Lauro- 

 cerasus, and others. 



* Plitt, C, ' Beitr. z. vergleich. Anat. d. Blattstieles d. Dikotyledonen,' 52 pp. and 

 1 pi., Marburg, 1886. See Naturforscher, xxi. (1888) p. 90. 



t Comptes Kendus, cvi. (1888) pp. 771-4. 



% Ann. Agronom., xii. pp. 497-521. See Bot. Centralbl., xxxiii. (1888) p. 137. 

 Cf. this Journal, 1887, p. 261. 



