108 



BOTANY. 



The young root and leaf now rapidly elongate, and burst 

 through the overlying cells, the former growing downward and 

 becoming fastened in the ground, the latter growing upward 

 through the notch in the front of the prothallium, and increas- 



FIG. 67. A, embryo of the ostrich fern just before breaking through the pro- 

 thallium, x 50. st. apex of stem. I, first leaf, r, first root. ar. neck of the 

 archegonium. B, young plant, still attached to the prothallium (pr.). C, 

 underground stem of the maiden-hair fern (Adiantum), with one young leaf, 

 and the base of an older one, x l. D, three cross-sections of a leaf stalk : i, 

 nearest the base ; in, nearest the blade of the leaf, showing the division of 

 the fibro- vascular bundle, x 5. E, part of the blade of the leaf, x y 2 . F, a 

 single spore-bearing leaflet, showing the edge folded over to cover the spo- 

 rangia, x 1. Gf, part of the fibro-vascular bundle of the leaf stalk (cross- 

 section), x 50. x, woody part of the bundle, y, bast. sfi. bundle sheath. 

 H, a small portion of the same bundle, x 150. I, stony tissue from the under- 

 ground stem, x 150. J, sieve tube from the underground stem, x 300. 



ing rapidly in size (Fig. 67, B). The leaf is more or less 

 deeply cleft, and traversed by veins which are continuations of 

 the fibro-vascular bundle of the stalk, and themselves fork once 

 or twice. The surface of the leaf is covered with a well- 

 developed epidermis, and the cells occupying the space between 



