Royal Microscopical Society. 269 



reflexed against the stem, probably pushed back by the descent of 

 the pendent branches; at their basal angles we also frequently 

 observe appendages or auricles formed of larger perforated cells. 

 The areolation of the stem leaves is ^vider than that of the branch 

 leaves, and the prosenchym cells of the lower part are often alto- 

 gether threadless, while one or more rows at the extreme base are 

 small, hexagonal, vesicular, and coloured red or yellow. 



The branch leaves are small, more densely reticulated, closely 

 imbricated over each other, and very variable in form and size ; this 

 variabihty, however, is greatest in the pendent branches, where both 

 they and their component cells become extremely elongated. 



Eussow, however, points out that the leaves on the centre of the 

 divergent branches are very constant in form in the individual 

 species, and that they all become narrower and more distant as they 

 approach the apex of the branch. Moreover, the 3 — 5 lowest leaves 

 at the base of the divergent branches are remarkably different in 

 form from those which succeed them, and stand midway between 

 them and the stem leaves ; the typical form of these intermediate 

 leaves is an irregular-sided, obtuse-angled triangle, and they are 

 always much smaller than the succeeding branch leaves ; the margin 

 of narrow cells which borders these leaves is widest at the base of 

 the longest side. The peduncular leaves, or those found at the 

 base of the naked branch which bears the fruit, differ from the 

 others both in form and structure, sufficiently to render their de- 

 scription necessary. 



As an aid to our examination of leaf structure, certain colouring 

 agents are of advantage in enabling us to obtain a better definition 

 of the dehcate textures of which the leaves are composed. Iodine 

 and sulphuric acid or a solution of biniodide of zinc, have been used 

 for this purpose, the latter of these being most convenient, an im- 

 mersion of the leaf for two to twenty-four hours being required. 

 Transverse sections of the leaves are also necessary in order to deter- 

 mine the relative positions of the chlorophyllose and hyahne cells ; 

 these are best prepared by immersing a branch in thick mucilage of 

 gum arabic, and when sufficiently dry, enclosing between two pieces 

 of elder-pith, and shces of the whole cut and placed in water. 



Anatomy of the Leaf. — Hedwig, in his ' Fundam. Hist. Nat. 

 Muse.,' i., p. 25 (1782), evidently noticed the composite character 

 of the Sphagnum leaf, for he mentions the large areolae, void of 

 chlorophyll, traversed by very fine vessels, running double, which 

 he thinks may possibly correspond to the ducts of flowering plants, 

 and these anastomosing vessels containing parenchyma. Molden- 

 hawer first pointed out the true nature of the two kinds of cells, and 

 the presence of threads and pores in the vesicular cells, and Yon 

 Mohl afterwards confirmed his views and elaborated the whole or- 

 ganization of the Sphagna. A Sphagnum leaf consists of a single 



