270 SUMMARY OF CURKENT RESEARCHES RELATING TO 



plasm is arranged in a network, the meshes of which are excessively- 

 close round the nucleus ; after stimulation, which is best effected by 

 the application of food, large spherical cavities appear in the mesh- 

 work, owing to the breaking down of some part of the plexus ; this 

 increases as time goes on ; the secretion may be sometimes seen to 

 escape in drops and to assume a rod-like form ; it is of a mucous 

 nature, and is due to the breaking down of the protoplasm. The 

 author describes the changes which take place in the stalk-cell after 

 electrical stimulus or feeding, and states that the body which he calls 

 the plastoid or "rabdoid," markedly decreases in size after long 

 stimulation, so that there are some grounds for believing that it con- 

 sists mainly of some reserve-material or some substance which is used 

 up during secretion. The normal effect of a regulated stimulus is a 

 swelling of the protoplasm and a loss of turgidity ; as the reaction is 

 uneq[ual in various cells there is a movement of the tentacle. 



Articulated Laticiferous Vessels.* — By observation on speci- 

 mens of Hevea hrasiliensis from Ceylon, Dr. D. H. Scott confirms his 

 previous conjecture that the laticiferous tissue of this genus agrees in 

 structure with that of Manihot, in consisting of true vessels formed 

 by cell-fusion, and not of inarticulated laticiferous cells, as in the 

 EuphorbiacesB previously investigated. The laticiferous tubes occur 

 on the phloem side of all the vascular bundles, and are limited to this 

 position, more being found in the parenchyma between the bundles ; 

 they form a complete anastomosing system. The absorption of the 

 transverse walls is not in all cases complete. Dr. Scott regards the 

 tissue as having a nutritive function. 



The author criticizes the classification of Euphorbiacese by Pax, f 

 founded on the nature of the laticiferous tissue. He accepts Pax's 

 view that the form of laticiferous tissue which consists of a series of 

 closed sacs, his "articulated tubes," gave rise to the inarticulated 

 laticiferous cells. The forms with closed laticiferous sacs may be 

 regarded as having given rise, on the one hand, to those with typical 

 laticiferous cells, as Euphorbia, on the other, hand to those with true 

 vessels produced by cell-fusion, as Manihot and Hevea. In Papa- 

 veracete we have an instructive series of transitional forms, illustrating 

 how the transition from sacs to vessels may have taken place. 



Medullary Rays of Conifers. | — Herr A. Kleeberg enters into 

 great detail respecting the structure and position of the thin spots in 

 the walls of the medullary rays and tracheids in Conifers. On the 

 cells of the medullary rays these spots occur in the form of circular 

 depressions, pores, or simple pits ; on the tracheids they are funnel- 

 shaped, the widest part of the funnel always facing outwards and 

 being closed by a delicate membrane ; these are the bordered pits. 

 There is again a difference in these bordered pits, according to whether 

 they are in juxtaposition with another bordered or with a simple pit. 



* Joum. Linn. Soc. Lond. (Bot.), xxi. (1885) pp. 566-73 (4 figs.). Cf. tWs 

 Journal, iv. (1884) p. 409. 



t See this Journal, v. (1885) p. 824. 



: Bot. Ztg., xliii. (1885) pp. 673-86, 689-97, 705-14, 721-9 (1 pi.). 



