DEVELOPMENT OF THE LEAF 



171 



grasses {a, in Vv^. 4().5 A). Instead of passin^^ around the stem, tlie 

 edges may come together between the leaf and the stem, so as to produce 

 a hollow tube, as in the Sarracenia. Let it next be assumed that the 

 apical portion, as well as the central-basal, enlarges, with little enlarge- 

 ment of the axial or lateral portions. We shall then get a form in which 

 a Lamina, or Leaf-blade, is superposed directly upon a Leaf-sheath, 

 Such a leaf, expanded, would appear as in Fig. 470, if the blade were 



46SA. 465 B. 4Y0. 47/ 



4r2 



Figures illustrating the origin and development of the parts of the leaf: Fig. 465 .-1. The grass-leaf: 

 a, the open sheath; h, the ligulc. 4()o B. Tlie sedge-leaf: a, the closed sheath. 466. The primordial 

 leaf, a mere scale. 467. The same, as equally developed in all parts. 4GS. The same, divided into its 

 different regions: o, the apical portion; b, basal portion; c and d, lateral portions with axial portion 

 between. 469. The same, undeveloped except the basal portion, which becomes a sheath to surround 

 the stem. 470. The same, with the apical portion also developed to form a blade, the lateral and 

 axial portions undeveloped. 471. The same, with the lateral portions developed into stipules. 472. 

 The stipules with their inner margins connate between the blade and stem, their outer connate around 

 the stem, forming an upper sheath or ochrea. In 40.5 .1 they are connate only by their inner margins, 

 between blade and stem, forming the ligule. (Ailaptid from work of A. A. Tyler.) 



but little developed, or it inight be deNcloped e(nially in botli ]iarts. 

 Both of these forms are fre(piently encountered. If now the hiteral 

 portions shall enlarge, the axial jjortioii not imich elongating, a lateral 

 appendage must result at the base ui)on eitiier side, as in Fig. 471. 

 These are the Stipules. If the stipules, insteatl of existing separately 

 in this way, shall incline together between the stem and the leaf, and 

 their inner edges cohere, it is clear that they must form a small blade 



