Frccma)i : obsek\'Atioxs ox coxstaxtinea. 183 



proach the large cells of the intermediate layer in form and size, 

 transitional stages between them being abundant (Figs. 8, 9, 10). 

 Tlieir average size is 55 mic. x 12 mic, but they may attain 

 75 X 16 mic. A cross section of the lower part of the frond, 

 tangential to its orbicular outline, shows in the central area at 

 more or less regular intervals corresponding to the external stri- 

 ation on the lower surface of the frond, a number of bundles of 

 greatly elongated cells, woven into strengthening bundles (Figs. 

 7, 8, 9). In the lower region the general course of these 

 bundles is radial in the frond. Divergence from this course is 

 found in the upper part so that a tangential cross section of the 

 frond shows some of these bundles in longitudinal or oblique 

 section (Fig. 9). These filaments are articulated; the cells of- 

 ten attain a length of 325 mic. They average about 8 mic. in 

 breadth. Thin sections of the frond often contain clean-cut cir- 

 cular spaces where the bundles of elongated cells have been 

 pulled out, showing the compactness of the bundles and indicat- 

 ing for it a strengthening function. The bundles vary in size; 

 the striations on the lower surface of the frond mark only the 

 largest bundles. 



b. The typical cells of the intermediate area are spherical 

 and average 46 mic. in diameter. They are packed with Flor- 

 idian starch granules which turn brownish with a weak KI so- 

 lution of iodine and finally purple or violet in a strong solution. 

 Those cells toward the surface of the frond contain ordinarily a 

 few chromatophores, usually in the end near the surface. The 

 cells of the intermediate layer shade off towards the surface into 

 the cortical cells. 



c. The cortical cells are characterized by a compact pseudo- 

 parenchymatous grouping in which the long diameters of the 

 but slightly elongated cells are perpendicular to the frond sur- 

 face. Many of the cells are approximately cylindrical or pris- 

 matic. The external layer is of a sufficient regularity in struc- 

 ture and form to recall forcibly an epidermal layer. In these 

 the outer wall is rounded. The cells of the cortical layer con- 

 tain but a small amount of starch, and this is found in the cells 

 adjoining the intermediate layer. Chromatophores are, how- 

 ever, abundant and more numerous toward the frond surface. 

 Almost all of them are to be found in the first three or four 

 rows of cells from the surface (Fig. 10), but some are found in 

 still deeper layers. They occupy, in the great majority of 



