7^4 



LECTURE XT.T. 



indeed that the reproductive organs of the Flowering-plants give to the uninitiated 

 the impression of having not the remotest similarity to those of the Cryptogams. 

 Nevertheless, my short description will show that from the reproductive organs of the 

 simplest Algae up to those of the most highly developed Flowering-plants all con- 

 ceivable transitions exist, leaving no doubt whatever, that (with the exception of a few 

 Algas and Fungi) all the reproductive organs in the Vegetable Kingdom are to be 

 referred to a single type, the clearest expression of which is found in the IMosses and in 

 the majority of the Ferns and Equisetums. And what may probably be termed the 

 most astonishing result acquired during the last forty years is the fact which will 

 shortly become clear, that the reproductive organs of the Flowering-plants, while in a 

 certain sense the most highly organised it is true, are in another sense again simply 

 reduced and degenerated forms. 



Approaching the matter more closely, and starting from the clearest cases, as 

 exempHfied in a large number of highly-developed Algse, some Fungi, all Mosses 

 and in most Vascular Cryptogams, there are always produced in the course of the 

 developmental history of such a plant two kinds of organs of reproduction, viz. 

 sexual organs, and asexual organs (Sporangia). 



The sexual organs are male or female ; the male organs produce zoosperms 

 (antherozoids), the female organs oospheres. In the present state of science it would 

 therefore be the simplest and most accurate plan to denote all male organs Spermo- 

 gonia and all female organs Oogonia, in contrast to the Sporangia which produce the 

 asexual reproductive cells — Spores. However it will scarcely be possible to establish 

 this simple nomenclature as yet, since a series of different names for the same organs 

 have become naturalised in different subdivisions of the Vegetable Kingdom. 



As already stated, there occur in the life-history of a plant of the above-named 

 subdivisions both sexual and asexual reproductive organs, and this in such a way 

 that by the co-operation of the male and female sexual organs, or to put it shortly by 

 means of the fertilisation of an oosphere, a plant-structure of some kind is produced : 

 this in its turn gives rise sooner or later, often as the result of very protracted processes 

 of growth and configuration, to a plant-structure of totally different organisation, on 

 which at last sporangia again make their appearance. The entire process of develop- 

 ment of a plant of this kind constitutes an alternation of generations, as it is shortly 

 termed. This consists then, according to what has been said, in the whole life-history 

 of a plant being divided into two chief sections. The developmental-history is twice 

 commenced from a reproductive process ; once with the germination from asexual 

 spores, the other time with the development of an embryo from the fertilised 

 oosphere, and — a point of extreme importance — the phase of life of the plant in 

 question which proceeds from the germination of the spore results in quite other 

 relations of organisation than the other. As a rule higher organisation is attained 

 in that phase of life which proceeds from the fertilisation of the oosphere. 



Such is, briefly, the meaning of the phrase ' alternation of generations.' 



If we now consider the mode of reproduction in some other Algse and Fungi, 

 there is found more or less agreement in the relations of the alternations of generations 

 described; some forms, however, can scarcely be referred at all to these schemes. 

 In the case of a few highly-developed Vascular Cryptogams, to which the Coniferae 

 and their allies are directly related, on the other hand, we meet with very complicated 



