« LECTURE I. 



It is however necessary yet to refer to some other points of general significance. 

 We seek the characteristic properties of organs, from our point of view, not in 

 their outward form, not even especially in their visible anatomical structure, but, as 

 already stated, in their manner of reacting to external influences, or of being irritable : 

 and this depends, as we shall yet see in what follows, less upon the external form and 

 anatomical structure, than upon those invisible relations of structure which are usually 

 termed molecular, and in the sense of chemistry, atomic. This implies, however, 

 that the characteristic similarities and differences of organs depend upon their 

 material constitution. From general scientific principles, we must assume that to 

 each visible external difference of the organ, there corresponds also a difference of 

 its material substance, exactly as we regard the form of a crystal as an expression 

 of the material properties of the crystallising substance. In our time of advanced 

 scientific knowledge, it might appear, strictly speaking, scarcely necessary to lay 

 special stress upon this principle; but the thoroughly scholastic way of thinking, 

 which, coming from former centuries, has been kept alive up to the most modern times 

 in the region of botanical morphology, makes it seem still advisable to devote a few 

 words to the matter. As late as the year 1880 one of the most renowned German 

 botanists, from the stand-point of these antiquated views, used the following words in 

 an academical address: "The figure of the entire organism, which will only be realised 

 in a material form in the future, already operates virtually in the present, as a motive 

 cause, before and during the development of the parts, just as does the plan accord- 

 ing to which the builder places his blocks." Such a mode of looking at organic forms 



the general, so-called morphological conceptions, and yet nobody ventured to form of them a special 

 category of organs, in contradiction to the obsolete doctrine of metamorphosis. 



In the present state of our knowledge, however, we have without doubt to take as the typical 

 reproductive organs of the whole vegetable kingdom, on the one hand sporangia, on the other the 

 archcgonia and antheridia of the Mosses and Vascidar Cryptogams. It would be ridiculous to wish 

 to arrange these under the morphological conception, leaf or stem ; we have here to do, rather, with 

 two groups of organs, well characterised physiologically and morphologically, viz. sporangia and sexual 

 organs. In the comparison of the Algae and Fungi with the Muscinens and Vascular Cr)'ptogams, it is 

 shown at once, not only that the proper spores of both groups correspond to one another, but also 

 that the so-called oogonia of the Thallophytes, are rudimentary simpler archegonia, and the same 

 holds good with respect to the antheridia. On the j)ther hand, following up the sporangia and 

 sexual organs of the Vascular Cryptogams into the clashes of the Gymnosperms and Angiosperms, 

 progressive degenerations of them, and a remarkable combination of the sexual organs with the 

 spores are found. That the pollen-grains correspond to the male microspores, the embryo sacs to the 

 female macrospores of the higher Cryptogams, is now generally accepted, after this relation had 

 long been established by Hofmeister and myself. Numerous more recent works bearing on the 

 history of development, especially those of Goebel, leave no doubt that the anthers, as well as the 

 ovules, are true though reduced sporangia, &c. 



Since I shall return to these matters later on, what has been said is only to serve to emphasize, 

 in connection with the division of the vegetative organs into root and shoot, that two peculiar 

 groups of organs stand opposed to them, viz. the sporangia and sexual organs, in their typical form 

 as archegonia and antheridia. We have thus to distinguish hve categories of organs : (I) the vege- 

 tative organs — (i) root and (2) shoot; (II) the reproductive organs — a asexual sporangia and 

 spores (3), b the sexual archegonia (4) and antheridia (5). All other forms of organs are rudi- 

 mentary or reduced organs of these groups. 



I have good reason for entirely discarding the term ihalhis. In the first place, the Greek word 

 6a\\os means simply shoot ; and, secondly, the thallus of the Algte and Fungi, taken purely as 

 a matter of fact, according to the customary view, is simply characterised by the want of leaves, 

 although the morphologists are by no means able to say what a leaf really is. 



