ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 409 



using the fibres of the nettle for technological purposes ; and the same 

 objections apply to Laportia piistulata, which has been attempted to be 

 naturalized in Germany from North America. 



Laticiferous Tissue of Manihot Glaziovii (Gear a Rubber).* — D. 

 H. Scott describes the laticiferous tissue of Manihot Glaziovii, and states 

 the result of his observations to be that in Manihot the laticiferous 

 tubes are not cells as in the members of the order Euphorbiacese 

 hitherto investigated, but vessels, agreeing in most points of distribu- 

 tion, structure, and development with those of the Cichoriaceas. 



At the same time this high development of the laticiferous system 

 is not inconsistent with the presence of numerous large and well- 

 developed sieve-tubes. Hence the prevalent views as to the mutual 

 substitution of these two classes of organs are, to say the least, of 

 limited application. Dr. Scott considers it probable that even within 

 a comparatively narrow circle of relationship the development of 

 laticiferous tissue has had more than one starting-point, and he is 

 disposed to assume a distinct origin in the order Euphorbiaceae for 

 the laticiferous cells and for the laticiferous vessels. 



Laticiferous Tissue of Hevea spruceana.f— D. H. Scott describes 

 the laticiferous tissue in the stem of Hevea spruceana to be similar in 

 its general distribution to that in Manihot, and though his observations 

 are not yet complete, its structure seems likewise to take the form of 

 laticiferous vessels and not cells. 



Development of Root-hairs.J — E. Mer has made a fresh series of 

 observations on the conditions favourable for the development of root- 

 hairs, and retains his previous opinion, in opposition to the conclusions 

 of Schwarz, that it is promoted by retardation of the growth of the root. 

 If grains of lentil are made to germinate on the surface of water fixed 

 on a float made of cork, the growth of the rootlets is at first slow. 

 They grow either obliquely or horizontally, or even rise towards the 

 surface of the water, and become covered with long hairs. As their 

 length increases they are more governed by geotropism, and grow in a 

 more vertical direction. The hairs with which they are covered then 

 become gradually shorter. The seeds of the pea, oat, and wheat 

 present similar phenomena. The rootlets which spring from the 

 bulb-scales of the onion are generally destitute of hairs, whether 

 developed in water, moist air, or the soil. But, if allowed to grow for 

 a time in moist air, until their growth has become retarded, a tuft of 

 hairs will make its appearance at the extremity of each. 



Symmetry of Adventitious Eoots.§ — Adventitious roots may 

 spring either from a node, in connection with a leaf or axillary bud, 

 or from an internode. Nodal adventitious roots are classified by 

 D. Clos as follows : — 



1. Later o-foliar. From the edge of a leaf, either on one side 



* Quart. Journ. Micr. Sci., xxiv. (1884) pp. 194-204 (1 pi.). 



t Ibid., pp. 205-7. 



X Comptes Kendus, xcviii. (1884) pp. 583-6. Of. this Journal, ante, p. 79. 



§ Ibid., xcvii. (188^) pp. 787-8. 



