292 SUMMARY OF CURRENT RESEARCHES RELATING TO 



laticiferous tubes — that their contents are reserve substances, or that 

 advocated by Mdlle. Leblois, that they are excretory products. His 

 observations, made chiefly on species of EuphorbiaceaB, confirm the former 

 and more prevalent theory. The following are the chief reasons assigned 

 for this conclusion. The composition of the latex, which contains 

 peptons, starch, sugar, fatty substances, tannins, resins, and calcium 

 malophosphate, is that of reserve products which the plant stores up for 

 future use. The wide distribution of the laticifers in the leaf, their close 

 connection with the chlorophyll tissue, and certain physiological experi- 

 ments, tend to show that the latex is drawn from the leaf, and is thence 

 distributed by the laticifers, as is shown by their relation to the xylem- 

 vessels and the reserve-parenchyme. This view is also supported by the 

 reduction of the parenchyme of the veins of the leaf when the laticiferous 

 apparatus is largely developed. 



Formation of Sieve-tubes in the Roots of Dicotyledons. * — From 

 the examination of species belonging to a number of different families, 

 G. Chauveaud concludes that the process is essentially the same in 

 Dicotyledons as in Monocotyledons. Primary sieve-tubes are formed, 

 which are either replaced by others, or, less often, retain their existence 

 alone. The primary sieve-tubes are formed by the septation of a 

 mother-cell, producing the sieve-tube and its sister-cell. When the 

 septum which divides the mother-cell is inclined at an angle of 45° on 

 the diametric plane passing through the axis of the sieve-tube, this 

 latter assumes a characteristic lozenge form (Ranunculus, Lamium, 

 Auricula, &c). When the septum is tangential, the sieve-tube is 

 pentagonal, and is superposed on its sister-cell in a regular manner 

 (RapTiani strum, Trapa, vtc). When this septum has a different orienta- 

 tion, the detached sieve-tube assumes no special appearance, and it can 

 be recognised with certainty only when it acquires its maximum dif- 

 ferentiation. 



Duramen and Healing-Tissue. f — According to A. Will, the sub- 

 stance found universally in the colls of healing-tissue (Schutzholz, 

 Wundholz), is not a gum, but a bassorindike subtance formed in a special 

 layer, the bassorinogenous layer, closely applied to the inner cell-mem- 

 branes, and formed from the protoplasmic cell-contents. A similar 

 substance is also usually, but not invariably, present in the cells of the 

 duramen. The colouring matter of coloured woods is a mixture of 

 various substances, gums, resin, oil, &c. A similar substance is con- 

 tained in the tbyllse, except in Guaiacum officinale, where it is replaced 

 by resin. 



New Type of Transition from Stem to Root.} — Miss Ethel Sargant 

 describes a new type of transition from stem to root in the vascular 

 system of seedlings, distinct from the three laid down by van Tieghem, 

 which occurs in the wild hyacinth and some other Monocotyledons. Its 

 characteristic feature is that two bundles only enter the hypocotyl which 

 passes into a root with tetrarch symmetry from the beginning. The 



* Ann. Sci. Nat. (Bol), xii. (1900) pp. 333-94 (4 pis.). Cf. this Journal, 1898, 

 p. 439. 



t Beitr. z. Kenntn. d. Kern- u. Wundholzes, Bern, 1899, 92 pp. and 3 pis. See 

 Bot. Centralhl., lxxxv. (1901) p. 295. 



I Ann. of Bot., xiv. (1900) pp. 633-8 (1 pi.). 



