The Microscope. 131 



Fiinaria, by embedding in elder-pith or other suitable material, 

 and examine under the microscope with a moderate magnifi- 

 cation, W6 find in addition to the outer layer of thickened cells 

 and interior large-celled tissue, a central bundle of very narrow 

 thin-walled cells, usually not sharply defined. "■ This central 

 bundle is said not to possess any of the strengthening functions 

 of a true vascular bundle, but to serve merely for the conduc- 

 tion of water. Its cells contain nothing but a watery fluid with- 

 out starch grains, oil, or protoplasm. In genera which have no 

 such central bundles, like Dicranuyn, or Leucobryum, the epidermal 

 tissue of the stem and branches with its perforated cells, forms 

 a similar capillary apparatus." If we examine a similar cross- 

 section of the stem of Polytrichum we find that the cell-walls of 

 the central bundle are not only much thicker than in Fanaria, 

 but that there are also extra-axial bundles, and in some cases 

 bundles of thin-walled cells have been found passing obliquely 

 through the stem, connecting the leaves with the central bundle ; 

 thus showing an increasing tendency to specialization of struc- 

 ture, and indicating that the mosses undoubtedly possess rudi- 

 mentary fibro-vascular tissues. 



The beginning of a leaf is a broad papillose bulging of a cell 

 of the stem, which becomes divided from the parent cell by a 

 septum, and continues to grow and subdivide until the full- 

 grown leaf is formed. 



If a leaf of Funaria be cut or scraped from the stem, and 

 placed in a drop of water under the microscope, it will be seen 

 to consist (excepting the margin and a band lengthwise through 

 the middle), of a single layer of cells, all of which contain 

 chlorophyll grains. This leaf will illustrate the general struc- 

 ture of the leaves of mosses, most of which consist principally 

 of a single layer of chlorophyll-bearing cells. In the Sphagnaceas, 

 however, and in Leucobryum, the cells are of two different kinds, 

 one large and empty, the other very small and containing chlo- 

 rophyll, thus giving the leaf a light yellow-green color. " In 

 Sphagnum the green cells of the leaf-blade are all connected to- 

 gether and form a network with elegant, bent walls, whose 

 meshes are occupied each by an empty cell. The green cells 

 serve for the assimilation of carbon, the empty ones (like those 

 of the stem) for conducting water." Generally the marginal 

 •cells of the leaf, and those of the central band, when that is 



