STRUCTURE OF MODIFIED SHOOTS 133 



leaves. Examine these carefully with a pocket lens. 

 Dissect off one or two leaves very carefully and note that 

 each is attached to the axis by a sheathing ring (Fig. 84, 4). 

 Cut a leaf across the middle and examine the cut surface, 

 and note the back-rolled margins and thick midrib 

 (Fig. 84, 5). The cells covering the midrib are crowded 

 with starch grains which are used up as the leaf grows ; 

 these cells enlarge, lose their contents and become filled 

 with air ; they then reflect light from their walls and give 

 rise to the familiar white streak of the adult leaf. In the 

 centre are three or more flower-buds (3), each surrounded 

 by a thin, membraneous sheath. Select one, remove the 

 sheath, and dissect the flower (6). Outside is a short, six- 

 lobed perianth (p), then come three stamens with short 

 filaments and large spear-shaped anthers (a). The ovary is 

 inferior and three-lobed, and above this is the long style 

 surmounted by three large, frilled stigma-lobes (3 st). All 

 the parts of the flower are present and are easily made out 

 in the bud. 



If flowering specimens (Fig. 84, 7 and 8), are examined, 

 considerable changes will be noticed in the corm. At the 

 base of the flowering shoots we see the beginning of a new 

 corm (8 c.3), formed by the thickening of the internodes 

 between the lower leaves. These leaves have become 

 withered and dead, and their ring-like bases form mem- 

 braneous scales around the young corm. The old corm 

 beneath (8 c.2), has given up much of its food-reserve of 

 starch, and eventually will collapse into a dead, shrivelled 

 mass. Thus new corms arise as thickenings of the stem of 

 an axillary bud of the old corm. In Fig. 84, 8 this relation- 

 ship is shown, but in this case we can detect the collapsed 

 remains of the still older corm at the base (c.i). When 

 the old corm is cast off, a scar is left (Fig. 84, 9) at the base 

 of the new one. This is a branch-scar, but, unlike the 

 shoots previously examined, the new branch in the Crocus 



