28 BOTANY part i 



The Stem op Axis of the Shoot 



According as the axis of a shoot remains herbaceous or becomes 

 hard and lignified, a distinction is drawn between an herbaceous 

 and a woody stem. A long leafless shoot arising from a rosette of 

 radical leaves and producing only flowers is called a scape. The 

 hollow jointed stems of the Gramineae are termed grass-haulms, 

 and should be distinguished from the similar stems or haulms of the 

 Juncaceae and Cyperaceae, which are unjointed and filled with light 

 porous pith. Plants with short swollen stems, being apparently stem- 

 less, are described as ACATJLESCENT. The actual stem of such acaul- 

 escent plants may be thickly clothed with leaves throughout its entire 

 length, as in the case of the Agave, or it may bear leaves only at its 

 apex, as in the Cyclamen. Stems are also distinguished as round, 

 elliptical, angular, etc., according to their appearance in cross-section. 



The Leaf 



Development of the Leaf. — The first appearance of the leaf as a 

 lateral protuberance (Fig. 17,/) on the vegetative cone of the shoot 

 has already been referred to (p. 18). In a transverse section 

 through the apex of a shoot (Fig. 29), the origin of leaves as lateral 

 protuberances is more evident than in a longi- 

 tudinal section. The embryonic leaf rudiment 

 generally occupies but a small portion of the 

 periphery of the vegetative cone ; it ma}', how- 

 ever, completely invest it. In like manner, 

 when the mature leaves are arranged in whorls," 

 the developing protuberances of the rudimentary 

 leaves may, although this is not usually the case, 

 form at first a continuous wall-like ring around 

 the growing point ; a,nd only give rise later to 

 the separate leaf rudiments. Leaves take their 

 origin only from such parts of a plant as have 

 remained in an embryonic condition. To this 



Pia. 29.— Apical view of the . . . 



vegetative cone of a shoot rule there are no exceptions. A leaf never 

 of Emnymus japonicus. arises directly from the older parts of a plant. 

 (x 12,) In cases where it apparently does so its develop- 



ment has been preceded by the formation of a growing point of a new 

 shoot. When it first appears on the vegetative cone a rudimentary 

 leaf resembles an embryonic shoot, but a difference soon manifests 

 itself, and the shoot rudiment develops a vegetative cone and lateral 

 protuberances for the formation of leaves. The growing point of 

 a shoot has usually an unlimited growth, while the growth of a 

 leaf is LIMITED. A leaf usually continues to grow at its apex for a 



