36 DOUGLAS HOUGHTON CAMPBELL ON THE 



A vertical section ol" the mother-cell at this time shows that it is somewhat elevated 

 above the surrounding cells, and is also somewhat deeper. The mother-cell i,s first di- 

 vided by a longitudinal wall, pai-allel to the axis of the lobe of the pinna, the nucleus 

 shoAving evident signs of division before any wall can be detected. By the time that the 

 division Avail is complete, the stoma has assumed nearly the oval form of its com])leted 

 condition, but the space between the guard-cells is wanting. This is formed by the di- 

 vision walls splitting through the middle. Vertical sections show that the air-space be- 

 neath the young stoma is small, but as the leaf grows, the space rapidl\' enlarges and 

 finally reaches considerable size. In the meantime, the walls around the opening of the 

 stoma become thickened, and the whole stoma enlarges. The chlorophyll-granules, which 

 ai'c indistinct in the young stoma, increase rapidly in size and number, and fill up nearly 

 the whole of the guard-cells. Those in the mature stoma are elongated-kidney-form, 

 but tli(* ends are only slightly rounded, so that the Avhole stoma is almost perfectly elHp- 

 tical in outline. The accessory cell, which at first had a smooth outline, acquires the sin- 

 uous outline of the other epidermal cells, and can only be distinguished from them by its 

 position. 



There are produced from the surface cells of the young leaf gi-eat numbers of hairs. 

 In the youngest leaves they are mostly glandular, the terminal cell being much enlarged 

 and pear-shaped, and filled Avith a densely gramdar but colorless mucilaginous secretion 

 which is somcAvhat troublesome in the study of the young leaf. Such glandular hairs 

 can be traced up to Avithin a very short distance of the tip of the leaf, before any of the 

 tissues are clearly differentiated. On the older pai'ts of the leaf, A\dien the epidermal cells 

 have assumed their characteristic form, but before they are full groAvn, both simple and 

 glandular hairs are developed, but the latter differ from those just described in regard to 

 the contents of the terminal cell, the contents being dark broAvn and apparently resinous, 

 instead of colorless mucilage. AVhen the leaf is unfolding, but not fully groAvai, these 

 glandular hairs arc so numerous as to give a rusty appearance to the petiole and loAver 

 surface of the leaf. 



Besides the hairs, there are formed upon the basal parts of the petiole of the J^oiing 

 leaves, and also upon the groAving point of the stem, large numbers of scales, whose first 

 formed cells elongate rapidly, no longitudinal Avails being formed in the extreme end ones, 

 so that the scale, AAdiich is broad at the base, tai^ers to a point consisting of a single cell, 

 or more commonly a row of two or three, Avhich become extraordinarily elongated. The 

 terminal cell develoi)s a gland filled Avith mucilage, but the growth of the scale contin- 

 ues long after the gland has been destroyed, and the cells sui^iiorting it dried up. The 

 scale grows at the base Avhich becomes broadly cordate, the cells there undergoing rapid 

 division. The upper cells gradually die and lose their contents, becoming dry and brown, 

 and finally the whole scale dries up, so that they form a thick broAvn chaff clothing the 

 bases of the jjetioles. 



In the yoimg plant the leaves have the one-third arrangement, but in the older ones 

 they are so croAvded that it is somcAvhat difficult to make out their arrangement; but Avith 

 care it may be seen that it is the same as described by Ilofmeister for Aspidium Filix- 

 mas, A. spinulosiim, and Asplenium FiUx-foemina, the five-thirteenth arrangement. 

 That is, the an<2:le of divergence is fiA^e-thirteenths, and the fourteenth leaf stands aljoA'c 



