i8 



THE SPHAGNACE^ OR PEAT-MOSSES OF 



properly some care is requisite, for the transverse sections must be 

 very thin and examined in water by a good light. We thus find 

 four modifications of the position of the chlorophyllose cells : — 

 I St, They may lie midway between the anterior and posterior 



surfaces of the leaf, being entirely enclosed by the hyaline 



cells, and the section shows that they are lenticularly 



compressed. 

 2nd. They may emerge between the hyaline on the anterior or 



ventral surface of the leaf, their section being triangular, 



so that they resemble a cushion or wedge pushed in 



between each pair of hyaline cells. 

 3rd. They may occupy the same position on the posterior or 



dorsal surface. 

 4th. They may emerge both in front and back — a condition 



observed only in a few species, and in this case their 



section is circular or oval. 

 The hyaline cells are more or less united by their adjacent walls, 

 and where they are applied to the chlorophyllose cells the walls of 

 the two become grown together ; in some species this combined 

 wall, as seen from the interior of a hyaline cell, is covered over 

 with minute deposits which take the form * lapillse, bars, or 

 crests, and by some authors have been errc jsly described as 

 remains of spiral fibres ; these are beautifully seen in our S. Austini 

 and papillosum, and in the foreign S, Portoricense and Herminieri, 

 The hyaline cells nearly always contain threads attached to 

 their internal walls, and these threads may form complete spirals 

 composed of one or several fibres, or they may be broken up into 

 rings, and fragments sometimes run across diagonally so as to unite 

 two spirals ; they are firmly and intimately united to the inner wall 

 of the cells, and often, e. g. in S. subseamdum, tightly lace up and 

 contract the cells at each turn of the thread, probably by contrac- 

 tion soon after its deposition. 



The fibrils are not always present in all the leaves ; thus in 

 S. fimbriatum they are wanting in both the stem and perichaetial 

 leaves, and some have them in one half of a stem leaf, as 6". 

 cuspidatum, where they are found in the upper part, but in 

 6*. macrophyllum no threads are found in any part of the plant. 



By some authors the presence or absence of threads in the cells 

 of the stem leaves has been looked upon as of specific value, but 

 a study of the varieties of the common species 6". acutifolium and 



