26 ANTHOLOGY: THE GENERAL NATURE OF THE FLOWER 



phytomers. This process is, however, sexual, and is called Repro- 

 duction. 



Composition of the Stem. — Roughly stated, the stem may be said to 

 consist of three portions: (1) A framework consisting of strands of 

 conducting vessels (54, g), associated commonly with fibers; (2) among 

 and around the last a quantity of soft non-fibrous tissue; (3) a covering, 

 membranaceous when young and changing greatly with age. 



Composition of the Leaf. — All these parts are extended into the leaf, 

 the first existing in a system of branching ribs or veins, the second as a 

 filling in the meshes of the former, and the third as a highly developed 

 skin-like covering, the epidermis. 



Parts of the Leaf. — Morphologically considered, the typical leaf 

 (B'ig. 3) consists of three parts which, like those of the stem, will be 

 considered in detail hereafter. The base (a) bears the Pulvinus or 

 organ of attachment to the stem, frequently 

 extended into an encircling sheath, and upon 

 either side a membranous expansion (b) called 

 the Stipule. The stem of the leaf (c) is called 

 the Petiole. The blade (d) is called the Lamina. 

 In some plants an additional organ, the Ligule, 

 develops as an appendage upon the face, being 

 a modification of the stipule (Fig. 465, A, b). 



Modification of the Structural Units. — If we 

 could observe the phytomers of such a tmg 

 during the process of formatioir in the bud 

 (Fig. 4) we should find them in a more and more 

 rudimentary condition towards its apex or center 

 until we reached an ultimate growing point (a), 

 where development had not yet manifested itself. 

 Yet this point would possess the power, under 

 proper conditions, of continuing the process of 

 development and growth of phytomers. It therefore may be said 

 to represent a certain amount of vital energy or potential growth. 

 Now, our fundamental ideas of flower structure rest upon the fact that 

 this vital energy or potential growth may be diverted from the produc- 

 tion of phytomers and leaves such as we have been considering and 

 may produce in their stead other structures in which resemblance to 

 and variation from them are mingled in variable proportions. These 

 new structures we then call Modified Phytomers and Modified Leaves. 

 The student should dwell upon this point until the exact meaning of 



Fig. 3. Leaf of willow, a, 

 pulvinus or foot; b, stipules; 

 c, petiole; d, lamina. 4. Dia- 

 gram of longitudinal aection 

 through bud. a, the growing 

 point. 



