LECTURE I. 



INTRODUCTORY REMARKS ON THE 

 PHYSIOLOGICAL ORGANOGRAPHY OF THE VEGETATIVE ORGANS. 



In the vegetable, as in the animal kingdom, we find extremely simply organised 

 forms, in which all the processes necessary for the maintenance and reproduction of 

 the individual are carried on in the limited space of microscopically small cells, in a 

 scarcely ponderable mass of vegetable substance. In such cases as the Yeast-fiingi 

 and many very small Algae, the body of the plant appears therefore, at least from the 

 exterior, of very simple construction, in the form of a cell, globular or ellipsoidal, 

 discoid, tubular, or of some other shape. In such cases nothing is to be seen of a 

 segmentation into different organs distinct from one another externally. With 

 increasing perfection of organisation, however, parts of various form, organs with 

 different functions, make their appearance as segments of the body of the plant, the 

 life-functions of which supplement one another; and this end is attained the more 

 completely the more each individual organ discharges but one function. With this 

 division of physiological labour, the perfection of organisation of a living being 

 increases. 



The most important division of physiological labour consists in this, that in 

 addition to the organs which serve for the maintenance of a plant already existing, 

 reproductive organs, i. e. such as have the sole object of producing new plants 

 of like kind, also arise. We may class together the former as vegetative organs in 

 contradistinction to these reproductive organs. 



Apart from quite isolated phenomena in plants of simple organisation, it is the 

 vegetative organs alone which constitute the whole body of a plant that strikes the 

 eye : the reproductive organs in the narrow sense of the word, the spores, oospheres, 

 antherozoids, pollen-grains, are always of microscopic minuteness, although larger 

 parts, which belong, strictly speaking, to the vegetative body, may assume special 

 forms and functions, by means of which they are enabled to act as accessory organs 

 in reproduction. To this category belong, for example, the parts of the flowers of 

 phanerogamous plants. 



Only later, when we are concerned more in detail with the physiology of the 



reproductive phenomena, shall we examine closely also the forms of the reproductive 



organs. As a preparation for the theory of nutrition, of growth, and of the phenomena 



of irritability, however, it suffices for the present to make ourselves acquainted with 



[3] B ^^ 



