96 MANUAL OF BOTANY 



of the stem,' with buds and leaves, when separated from the 

 parent and planted in soil, will, under appropriate conditions, 

 put out roots from the cut sui-faee, and thus replace the parts 

 missing and lead an independent life. Buds may arise from 

 wounded leaves or petioles under similar conditions. 



In this mode of reproduction the form of the plant from 

 which the new one is derived remains unchanged. Thus 

 sporophyte gives rise to sporophyte, gametophyte to gameto- 

 phyte, and there is no alternation of generations. 



Section II. 



ASEXUAL KEPRODUCTIVE ORGANS. 



The Spores. 



The relative dimensions of the sporophyte and gameto- 

 phyte in the different classes of plants varies considerably. 

 There is, however, a somewhat regular series in both. The 

 morphology of the gametophyte will be treated of in a subsequent 

 chapter. The sporophyte can be distinguished only with 

 difficulty in the Algffi and Fungi, and many of these plants do 

 not possess one ; in the Mosses the sporophyte is the tlieca, 

 capsule, or sporogonium, which is developed from a fertilised 

 cell at the apex of the leafy shoot. In the Ferns the sporophyte 

 is the so-called plant, as it is in the Equisetums and Club mosses. 

 The Phanerogams show the sporophyte in its best development, 

 the whole plant as we see it representing that phase. 



The reproductive organs of the sporophyte are specialised 

 cells known as spores. These are generally single cells, usually 

 furnished with a tough, sometimes much-thickened coat, en- 

 closing, in addition to its living substance or protoplasm, various 

 nutritive materials, such as starch, sugar, oil, &c. The spore- 

 coat in some cases is thin and delicate. Spores are produced in 

 various ways in different plants, but are usually found in special 

 receptacles known as sporangia. 



As we have already said, similar asexual cells are very 

 generally borne upon the gametophytes of the Algas and Fungi. 

 These are known as gonidia, and the structures in or on which 

 they arise may be called gonidangia. 



In the cases where the spore has no outer wall, it must be 

 regarded as a naked piece of protoplasm. It is then frequently 

 furnished with a number of vibratile threads at one or more 

 points of its surface, by which it can move freely about in 



