SELECTED NOTES. 283 



embraces the stem. This will be better understood by reference 

 to Fig. 19. 



Many of the Diato7nacece are characterised by having a zone 

 of very lax tissue at the base of the leaf, and a very small- 

 celled areolation in the upper part, see Fig. 29. In some of the 

 TortulacecE the lamellae (referred to before in Polytrichacece) are 

 decurrent, and in the form of a membrane, instead of in sub- 

 algal thread, as in Fig. 18. Tortula lamellata is known as having 

 four of these decurrent bmellae on the upper third of the leaf, as 

 shown in Fig. 21. 



The leaf-cells of the sphagnum exhibit a very curious de- 

 parture from the ordinary type, for instead of being small and 

 polygonal, as (with a i^w exceptions) is the rule in most mosses, 

 they are large and elongated. They exceed in size the cells of 

 Pterygophyllum^ they do not contain any chlorophyll, but have a 

 loosely coiled, spiral fibre of secondary tissue in their interior. 



Their cell-walls are pierced by large rounded apertures, by 

 which thin cavities freely communicate with one another, as is 

 sometimes curiously evidenced by the passage of animalculse 

 which make their habitation in those small chambers. Between 

 these coarsely spiral cells are some thick-walled, narrow, elon- 

 gated cells, containing chlorophyll ; these, which give the leaf its 

 firmness, do not, in the very young leaf, differ much in appearance 

 from the others, the peculiarities of both being evolved by a 

 gradual process of differentiation. A half-inch objective will 

 suffice for their examination. Further information may be gather- 

 ed from Dr. Dallinger's edition of Carpenter on the Microscope, 

 pp. 598-599, but the great work on the subject is Braithwaite's 

 Sphagnacece. 



The leaves of mosses present the best j-jossible method of 

 studying in the living state the manner in which the chlorophyll is 

 packed in the cells. The leaves of Funaria are usually chosen, 

 but the "prothallia" of ferns are equally good for the same 

 purpose. The lamina of mosses being one cell thick, there is 

 consequently no under-portion to obscure the vision, and the 

 grains are larger than in most plants of a higher development. 



I feel a degree of hesitation in directing attention to a subject 

 so elementary, but the division of the individual grain into two 



