IN VEGETABLE BIOLOGY. 613 



cesses, the agents of axial-siphonal continuity — are very dark in 

 colour, but, when boiled in caustic potash and stained with chlor- 

 iodide of zinc, indirect continuity can be made out without much 

 difficulty (fig. 51). 



Halubus equisetifolius. — But if the large cells of DeJesseria 

 alata and Polysiphonia nigrescens are in great measure composed 

 of membrane, the row of larger cells, of which the axes of 

 Halurus equisetifolius are made up, show the opposite condition 

 of things. The protoplasm in these cells is placed in continuity 

 by means of a relatively small broadly-contoured ring placed at 

 or near the centre of the wide flat wall of partition (fig. 52). 

 Upon the membrane lies protoplasm in such quantity that the 

 perforations are masked ; the semi-profile view of the figure, 

 however, shows that some at least of the threads are circum- 

 fesential. 



Each of the axial cells of a branch bears near its top a whorl of 

 frequently ramifying branches composed of a single row of small 

 cells several times longer than broad. With the basal cell of every 

 branch the axial cell communicates through a small perforated 

 ring ; and a similar but smaller ring is placed between every pair 

 of cells of the branch. The origin of these rings seems to be the 

 same as that of those hitherto described ; that a membrane is 

 developed in them very early is shown by fig. 53, which repre- 

 sents the membrane between the ultimate and penultimate cell 

 of a branch from a preparation boiled in caustic potash for a 

 minute or two, and then stained with picric blue. From the 

 branchlet's basal cell ultimately descend corticating fibres re- 

 sembling in structure the branches themselves. The connections 

 between the cells of these are similar to those between the cells 

 of the branch. 



Ballia calliteicha. — If one of the main branches of this 

 species be examined a short way above the point where cortica- 

 tion begins, the junctions of its single series of axial cells will 

 present the appearance shown at fig. 54. It would seem at first 

 sight that, in accordance with Harvey's * description, the upper 

 cell protrudes into the lumen of the lower ; but, as Mr. Archer t 

 showed, the reverse is the fact : this can be ascertained without 

 much difficulty by cutting off the branchlets of an uncorticated 

 branch and turning the flattened axis through an arc of 90°. In 

 * In Hooker's ' Journal of Botany,' 184(1. 

 t Trans. Linn. Soc. 2nd ser. Bot. i. p. 211 ct scq. 



