8 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



variation from them are mingled in vari- 

 able proportions. These new structures 

 we then call Modified Phytomers and 

 Modified Leaves. The student should 

 here dwell upon this point until the exact 

 meaning of these terms becomes clear. 

 When hereafter he encounters, as he very 

 frequently will, a reference to some organ 

 being modified or transformed, it must 

 never be understood that it was first pro- 

 duced and then changed. The exact 

 meaning is that the change takes place in 

 the direction or exercise of the energy 

 which is to produce the modified structure. 



Such a diversion of energy may be 

 caused by accident, as seen in the so- 

 called *'Willow-cone" (Fig. 5), resulting 

 from an injury inflicted by an insect in 

 depositing its eggs in the centre of a bud. 

 A portion of the structures, having been 

 originated before such injury, will reach a 

 partial development, but further pro- 

 duction is checked and a distorted product 

 results. 



In the case which we have to consider 

 the modification dates from an earlie 



stage and is natural and physiological, in- 

 stead of pathological, as in the case of the 



r 



willow-cone. Fig. 6 represents one twig 

 after the fall of its leaves in the autumn. 

 Each bud is seen protected by its lowest 

 leaf, permanently enlarged and developed 

 Into a covering scale. At the base is seen 

 the scar of the leaf in the axil of which 

 the bud was developed. Fig. 7 illustrates 

 the twig in the spring after early growth 

 has enlarged the buds. In Fig. 8a the 

 covering scale has fallen, the branch has 

 developed, and its structure can be seen to 

 consist of a great number of very short 

 phytomers, each of the crowded nodes 

 bearing a scale (c) and in its axis (Fig. 9) 

 a peculiarly shaped body. That the scales 

 are modified leaves is proven not only by 

 their position, as previously explained, 

 and further explained in our study of 

 the leaf, but by the fact that in excep- 

 tional cases the branch will produce them 

 in a form intermediate between that of a 

 scale and of an ordinary leaf (Fig. 10, a). 

 Such being the case, anything produced 

 in their axils must, according to the same 

 laws of position, be modified branches. 

 We must therefore regard the body shown 

 in Fig 9 as a modified branch, one of a 



great many produced upon the parent 

 modified branch shown in Fig. 8. How 

 profound is the modification which has 

 taken place in the latter can be appreci- 

 ated from a consideration of its reduced 

 size, for it is now approximately full 

 grown. The great number of phytomers 



upon it, had they reached the form and 

 extent of development reached by those 

 in Fig. 1, would have produced a branch 

 many feet, or even yards, in length, 

 whereas in their present form they will 

 produce a structure only an inch or two 

 long. As we shall soon see, increased 

 complexity of structure has replaced the 

 greater amount of tissue growth of the 

 leafy branch. 



i 



III 



T] g, t. 



Fig. 7. 



Examining now the little modified 

 branch (Fig. 9) we observe that it presents 

 two uniform portions or halves, united 

 into a single body except at the tip, where 

 they are separate. In exceptional cases 

 we find this separation extended down- 

 ward, perhaps even to the base of the 

 body, and each of the separated portions 

 expanded, formed and veined very much 

 like a small leaf, which, in fact, it is. 

 The little branch a-d is then to be re- 

 garded as bearing two leaves which have 

 been developed in a united condition. 

 Upon dissection (Fig. 11) the body thus 



