368 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



historical abstract, from Henshaw in 1G65 to Correns, Rothert and 

 others in the present century. He criticizes all previous work on the 

 subject as deficient for want of a proper method of staining ; and 

 supports strongly his own process— the tannin-silver process devised by 

 Hortega, which he says he has employed for a year with surprising 



results, upon wood-vessels. The wall of 

 the vessel, apart from the thickening (to 

 which his investigation is especially 

 directed), he calls the "primary mem- 

 brane"; this stains a barely perceptible 

 violet. The thickenings (secondary mem- 

 brane) show three very distinct concentric 

 layers — namely, a very slender central core, 

 which stains nearly black'; this is en- 

 veloped by a fairly thick sheath which is 

 but little affected by the stain ; this iu 

 turn is surrounded by an exterior sheath 

 of similar or greater thickness, stained 

 with intensity intermediate between the 

 other two. Several figures are given, 

 making these points very clear ; and the 

 author has obtained similar results from 

 plants of widely differing affinity. He 

 urges the structure in question as con- 

 stant for all thickened wood-elements, 

 and attributes the differential staining to 

 the successive addition of various sub- 

 stances to the elemental cellulose. He 

 suggests analogy to the structure of starch- 

 grains, and confirms this in a striking 

 figure of some taken from the radicle of 

 Cicer arietinum, which he treated by the 

 same method. These show the same cen- 

 tral deeply-stained core, a surrounding 

 unstained part, and a moderately-stained 

 outer coat. The author concludes that 

 all such processes of organic development 

 by the successive addition of layers are 

 traceable to a few elementary chemical 

 substances, carbohydrates and their deriv- 

 atives ; and that a living cell, in the 

 meristematic state may, by this method of staining, reveal its ultimate 



Longitudinal section of a 

 spiral vessel of Iris ger- 

 manica, showing stain- 

 ing efiect. A., primary, 

 B.J secondary membrane. 



con- 



fate. Moreover, the constancy of the three layers suggests the 

 stancy of these substances in question in all cases — all being derivatives 



of the original cellulose of the primary wall. 



H. F. W. 



Anatomy of the Leaf of Lactuca saligna Linn. — Inan Cuesta 

 Urcelay {Boletin de la Real Sociedad Espanola de Historia Natural, 1918, 

 426-8, 4 figs.). A brief account of a peculiar form of hairs that occur 

 upon the leaf of certain Compositse. These structures have been 



