426 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



the percentage of glucose was 96 '6. lu the dry nectar of Hoya carnosa 

 the percentage was 12-24 of glucose and 87-44 of cane sugar. The 

 author states that nectar is destitute of formic acid, and that its com- 

 position varies considerably with the age of the nectariferous tissue. 



(4) Structure of Tissues. 



Thickening of the wall of parenchymatous cells.*— M. J. Baranetzki 

 states the following general conclusions as the results of a study of this 

 subject. The thickening of the soft parenchyma usually presents itself, in 

 its mature state, in the form of a network composed of separate strings 

 arranged in a definite manner. In the very young state of the cell-wall its 

 thickening has always the form of a delicate network, subsequent trans- 

 formation of which may produce a thickening in the form of punctations ; 

 the punctations of lignified cells have always the same origin. In the 

 walls of 2)arenchyma there may always be distinguished at least two, and 

 often three superposed systems of thickening layers, characterized by 

 special morphological peculiarities, viz. — a, primary membrane, alto- 

 gether continuous and homogeneous ; &, secondary thickening, having 

 at first always the form of a network, but subsequently transformed into 

 punctations ; c, tertiary thickening, sometimes in the form of broad 

 bands, sometimes of still continuous layers, which may then cover up 

 the punctations of the secondary system. 



The secondary and tertiary thickenings are produced by the successive 

 apposition of new layers on the inner surface of the cell-walL Those 

 walls which have only a secondary thickening appear never to become 

 lignified ; lignification commences only with the formation of the tertiary 

 layers, and depends on the fact that the protojilasm produces, along with 

 cellulose, certain other soluble substances which impregnate the cell-wall. 

 The direction of the strings of secondary thickening is determined by the 

 general direction of growth and by the form of the wall. The secondary 

 strings or bands are always adapted, by their form and arrangement, to 

 protect the cell-wall in the best j)ossible way against the pressure exercised 

 in the plane of the cell-wall itself. 



Endoderm of Senecio Cineraria. f — M. P. Vuillemin describes the 

 structure of the endoderm of tliis species, which closely resembles that 

 in S. caudatus. It originates, both in the stem and leaves, on the back 

 of the fibrovascular bundles. The oleiferous canal is formed at the 

 expense of a cell of the internal row. The outer row establishes the 

 continuity of the amylaceous layer in the leaf and of the layer of cells 

 with folded walls in the stem. 



Cambium of the Medullary Rays.| — On physiological grounds con- 

 nected with the storage of food-materials, and with the function of the 

 initial cells of the medullary rays, Herr A. Wieler contests Haberlandt's 

 view,§ that the cambium of the medullary rays is a secondary meristem. 



PoresoftheIibriformTissue.il— Dr. Emily L. Gregory describes the 

 various kinds of pore found in woody tissue, distinguishing between those 

 which are simple and those which are bordered. The principal genera 

 of 67 families were examined, among which there were only 8 in which 

 the libriform tissue contains both bordered and simple pores; 18 



* Ann. Sci. Nat. (Bot.), iv. (18SG) pp. 135-201. 



t Bull. Soc. Bot. France, viii. (1886) pp. 538-40. 



X Ber. Deuttich. Bot. Gesell., iv. (1886) pp. 259-66. 



§ See this Journal, 1886, p. 1009. 



II Bull. Torrcy Bot. Club, xiii. (1886) pp. 197-204, 233-44 (4 figs.). 



