348 MALE PERN. 



(2) the niesophyll, practically uniform and consisting of 

 more or less branched and star-shaped cells, separated by 

 large intercellular air-spaces ; (3) the lower epidermis ; 

 (4) stomata, present in the lower epidermis but very 

 rarely in the upper ; (5) vascular bundles, embedded in 

 the mesophyll, each bundle surrounded by a conspicuous 

 sheath (endodermis) and having the xylem nearer the 

 upper side of the leaf, instead of in the centre of the bundle, 

 as in the stem. This almost collateral structure of the 

 leaf -bundles can be well seen in sections of the leaf -stalk, 

 especially in the upper part. 



Remove strips of the epidermis from (1) the upper and 

 (2) the lower side of the leaflet; in both cases note the 

 very wavy vertical walls of the epidermal cells, which 

 have chloroplasts ; in the lower epidermis note the stomata, 

 with two guard-cells. 



489. Sorus and Sporangia (Fig. 86). Cut several 

 transverse sections of leaflets with sori. In one that has 

 passed through the centre of a sorus, note, in addition to 

 the structure of the leaflet, as given above, the following : 

 (1) the small cushion-like placenta, a mass of tissue 

 seated on a vein which sends a branch into it; (2) the 

 stalked indusium arising from the end of the placenta 

 and spreading out like an umbrella over (3) the stalked 

 brown oval sporangia. 



Also cut off several sori from a leaf, tease in water, 

 cover, examine. Note the simple structure of the in- 

 dusium. 



In both these preparations, note that sporangia in 

 different stages of development occur in the same sorus. 

 The mature sporangium consists of a fairly long stalk 

 (composed of either two or three rows of cells, and often 

 bearing a pear-shaped one-celled gland supported on a 

 long slender cell) and a capsule having the form of an 

 oval biconvex lens. 



The wall of the capsule is one cell thick, and the cells 

 round the edge, starting from the stalk and going over the 

 top of the sporangium half-way down the other side, are 

 large and thick-walled, forming the ring (annulus) ; each 



