OF ARTS AND SCIENCES. 



203 



plexity, for in the new blade just forming they are entirely absent. 

 Tiiey are saucer- or shallow bowl-shaped depressions, about 0.3 mm. 

 in diameter, 0.15 mm. deep, with a large number (60 to 70) of hairs 

 projecting from the bottom. The margin of the saucer has a sort 

 of rim projecting in over the edge of the depression, such as Ares- 

 (•lioug* describes for the Norwegian plant. 



Adult Forms. — Specimens collected by Dr. Parker at Nahant, on 

 .July 26, 1889, are shorter than the last, have no cryptostomata, are 

 of a darker color, and more leathery in consistency. Sections through 

 the various organs of some of these specimens show the arrangement 

 of tissues much as described in the last ; but show also that the walls 

 of all the elements of these tissues have undergone extensive thicken- 

 ings, and that the elements themselves are somewhat larger. It will 

 be well to glance, then, at the charges which have thus taken place in 

 the tissues of a plant more matured, but not yet fruited. Such plants 

 are common at Nahant in the middle and latter part of September. 



a. Limiting Layer. — In these plants the limiting layer is still 

 present, but is covered with a thick secretion resembling a cuticula. 

 The latter may be separated readily from the section, and then has a 

 pitted appearance where it has been parted from the rounded ends of 

 the cells. The cells of the limiting layer, both in stipe and in blade, 

 are usually somewhat elongated radially (cf. Fig. 24, L). Tiie very 

 outside walls and the cuticula give a yellow reaction with chloriodide 

 of zinc solution, but the inner walls turn a pale bluish. At the base 

 of most of the cells small cells may be seen in cross-section (cf. Fig. 

 24, a) which have recently been formed by tangential division. The 

 cells of the limiting layer always have dense contents and numerous 

 brown chromatophores, so that the section needs to be particularly thin 

 to show the cell structure without the use of clearing reagents. 



b. Cortical Layers. — The next layers differ in stipe and in blade 

 in the details. In the blade the cortical layer is not at all distinctly 

 divided into inner and outer, as seen in cross-section. In a longitudinal 

 section, however, the innermost cells are elongated and have hjqjhal out- 

 growths, while the outer ones are shorter and more irregularly placed. 

 In the stipe the outer cortex appears distinct in a transverse section, 

 from its cells being somewhat elongated radially and arranged in 

 radial rows, although it is not as plain in this species as it is in those 

 of the genus Laminaria. The cells of the inner cortex of the stipe 

 appear more nearly hexagonal in transverse section, and are not 



* Obs. Phyc, Part. III. p. 12. 



