REPRODUCTION. 629 



the sporogonium, which is the asexual generation in the life- 

 history. The body of this organism is not differentiated into 

 stem and leaves, but consists usually of a longer or shorter 

 stalk (seta) bearing a capsule (theca) in which the spores are 

 developed. When one of these asexually produced spores 

 germinates, it does not give rise to another sporogonium, but 

 to an inconspicuous, usually filamentous, structure, the protone- 

 ma, upon which are developed, as lateral buds, moss-plants 

 which bear sexual reproductive organs. In other words, the 

 sexually produced spore (oospore) always gives rise to the 

 sporophore (sporogonium), the asexually produced spore to the 

 oophore (moss-plant). 



This kind of life-history is not peculiar to the Muscineae, 

 but it can be more or less clearly traced in all the vascular 

 plants. In the Isosporous Vascular Cryptogams (Filices, 

 Equisetaceae, Lycopodiaceae), the asexually produced spore 

 gives rise, on germination, to a small inconspicuous organism, 

 destitute of vascular tissue, termed the prothallium, on which 

 the sexual reproductive organs are borne. The oospore, pro- 

 duced by fertilisation in the archegonium, gives rise to the 

 plant, consisting of stem, root, and leaves, which produces 

 the sporangia and spores. The prothallium, is clearly the 

 oophore, and corresponds to the moss-plant: the fully de- 

 veloped plant is clearly the sporophore, and corresponds to 

 the moss-sporogonium. 



In the heterosporous vascular plants (Rhizocarpae, Ligu- 

 latae, Phanerogams) the asexually produced spores likewise 

 give rise to prothallia, though they are rudimentary. The 

 microspore gives rise to a prothallium which is reduced to 

 a single antheridium, and which, with the exception of 

 Salvinia, among the Rhizocarps, and of the Phanerogams, 

 does not project from the spore. In Salvinia and in the 

 Phanerogams it projects in the form of a closed tube which 

 is known in the Phanerogams as the pollen-tube. Similarly, 

 the macrospore of these plants gives rise to a small pro- 

 thallium bearing one or more archegonia, which, in the 

 Rhizocarps extends beyond the limits of the spore but does 

 not become free from it; in the Ligulatae (Selaginella and 



