2 INTRODUCTION. 



vegetative organs. Having regard to the points of view established above, as well as 

 to considerations of the available space, the work has further to presuppose a know- 

 ledge of the morphology of members — otherwise called the general morphology of 

 plants, and general doctrine of the cell — and only to touch on these subjects as far 

 as may be necessary. 



Since the investigation extends over three great sections of the vegetable king- 

 dom, it will be our task to describe comparatively those phenomena, in which the 

 representatives of these sections correspond, or differ : that is, to offer a coinparative 

 anatomy of the vegetative organs. 



Under the term vegetative organs we include all those organs of the plant which 

 are not organs of reproduction, i.e. which do not, sexually or asexually, serve in the 

 production or direct preparation of germs : the term includes therefore those organs 

 which undertake the entire work of preservation of the physiological individual, and 

 which may take different parts in this work. 



In the plants in question, which always have members of many grades, those 

 of every sort and rank are to be found developed into vegetative organs : both those 

 belonging to the highest ranks, which are externally apparent, such as roots, leafy 

 shoots, with their internodes and leaves ; and of successively lower ranks, such as 

 definite groups of cells, and lasdy single cells, or the products of their metamorphosis. 

 But investigation show's that the adaptation to, and participation in vegetative duties, 

 that is, the development into organs of definite function, and corresponding structure, 

 is far the most commonly and definitely carried out for members of lower ranks, i.e. for 

 cells, and groups of cells, or the products of their m.etamorphosis. It is these which in 

 the first instance share among them the vegetative work, and assume a correspondingly 

 characteristic form and special structure. A member of higher rank composed of 

 them is only a vegetative organ of higher rank, inasmuch as it consists of them. The 

 structure characteristic of such an organ is determined by the structure and distribu- 

 tion of the organs of lower rank, which compose it. The vegetative structure in ques- 

 tion is not universally connected with definite members of higher rank. Equivalent 

 members, it is true, very often develope into equivalent organs : the functions of the 

 leaf, assimilation of carbon, transpiration, &c. are, for instance, usually deputed to 

 leaves : most roots are equivalent to one another in both relations. But, on the other 

 hand, the converse is not uncommon, that non-equivalent members are equivalent 

 organs. In many plants besides the leaves the internodes also, which are connected 

 with them, take part in the functions of the leaf : in others, with ' leaf-like ' stems, 

 the function and corresponding structure, which the leaves have lost, are transferred 

 to the stems. Trapa natans has part of the petiole developed into a swimming organ : 

 in the floating species of Desmanthus internodes of the stem, and in species of 

 Jussia^a certain roots assume this function, and corresponding structure. 



This being the case, the description of the structure of the vegetative organs 

 must start from the consideration of simpler forms, i. e. the cells. Since the investi- 

 gation of these separately is necessarily followed by that of their connection with 

 others, and of their arrangement into tissues of various grades, the structure of the 

 organs composed of these gradually becomes apparent. 



Those cells or their derivatives, which have the character of definite vegetative 

 organs, seldom occur, in the plants in question, singly between dihsimilar ones; 



