ON THE INTERCELLULAR RELATIONS OF PROTOPLASTS. 145 
ON THE INTERCELLULAR RELATIONS OF 
PROTOPLASTS.—IV. 
BY WILLIAM HILLHOUSE, M.A., F.L.S., ETC. 
(Continued from Vol. VII., p. 126.) 
Having at times probably a genetic relationship with sieve 
tubes are the articulated latex vessels, an interesting memoir 
on which was published in 1882 by D. H. Scott."' Dippelt 
had believed the resemblance to be sometimes carried to the 
extent of the presence of sieve-like perforations in the 
septa, as in <jheliclonium and Papaver, and of actual 
lateral sieve-plates in the same genera, thus producing 
intermediate structures between sieve tubes and latex 
vessels. It must, however, be borne in mind that 
the conception of a sieve plate has greatly developed 
since 1863. A sieve plate, as lias been fully noted earlier in 
this paper, has special structure besides its mere sieve-like 
perforation ; and while it is quite true that the septa of latex 
vessels are often perforate, and that not merely by one, but 
often by a group of perforations, they are large in size, 
irregular in outline, and altogether devoid of callus. 
Thus far, therefore, sieve tubes must be regarded as the 
only structures in which any approach to protoplasmic 
continuity (not bodily) had been universally recognised ; and 
even with these it must be especially remembered that the 
protoplasmic threads connecting the contents of the adjoining 
cells constituting the tubes are products of protoplasmic 
activity, and are not relics of initial unity. They are the 
last term of a series of resorption phenomena which manifest 
themselves in so many stages of vegetable development— 
the fusion of the conjugating canals in Zygnemaceae and 
Mucorime, the union of rows of cells into vessels and ducts, 
the anastomosis of cells in a latex system, the peculiar wood 
cells of the mistletoe (Viscum album). 
It remained for TanglJ to open up, in 1879, a new vista 
of possibilities in a memoir, in which he demonstrated the 
* D. H. Scott, B.A., “ The Development of Articulated Laticiferous 
vessels,” Q. Journ. Mic. Sc., 1882, pp. 136—153 and 1 plate. 
f Dippel, “ Entstehung der Milclisaftgefasse,” Verliandl. d. Ba- 
taafsch. Genootschap, &c., te Rotterdam, tom. XII., p. 3 (1863). 
t Tangl, “ Ueber offenen Communicationen zwischen den Zellen 
des Endosperms einiger Samen.” Pringsheim’s Jahrbiicher f. wiss. 
Bot. XII., pp. 170—190, and plates 4—6. 
