50 PART I. MORPHOLOGY. [ 15 



rounded tuberous gemmae are frequently formed on the protonema. 

 The prothallia of some Ferns (Trichomanes) are reproduced by few- 

 celled filamentous gemmae ; and that of Lycopodium Phlegmaria 

 by ovoid tuberous gemmae. 



In the Vascular Cryptogams and Phanerogams, vegetative 

 reproduction is generally effected by buds, the leaves or stem of 

 which have become swollen, serving as depositories for nutrient 

 substances. These buds may be subterranean, and then they 

 are of considerable size, when they are termed bulbs or corms 

 according to their structure (see p. 25) : or the buds may be 

 borne on a swollen subterranean stem (e.g. potato-tuber) ; or be 

 associated with tuberous roots (e.g. many terrestrial Orchids). 

 Sometimes they are aerial, being borne on the stem ; on ac- 

 count of their small size they are termed bulbils (e.g. Lilium bul- 

 biferum, Dentaria, Nephrolepis tuberosa, etc.). In Psilotum, 

 however, vegetative propagation is effected by small flattened 

 gemmae, oval in shape, and consisting of a few large cells forming 

 a single layer. 



2. Spore- Reproduction. The term spore is applied to a 

 specialised asexual reproductive cell which is capable, by itself, of 

 giving rise to a new organism. 



There are two principal modes of origin of spores, and all plants 

 produce spores in one or other of these modes. In the one, the 

 spores are formed from the protoplasm of any part, or of some 

 special part, of an organism ; in the other, they are formed by the 

 fusion of two masses of protoplasm derived either from two dis- 

 tinct organisms, or from distinct parts of the same organism. In 

 the former case they are said to be formed asexually ; in the latter, 

 they are formed sexually, the fusion of the two masses of proto- 

 plasm being a sexual process (p. 2) ; the organs concerned are 

 distinguished respectively as asexual and sexual, and are in all 

 cases confined to the shoot. 



The spore is generally a single cell, consisting of a nucleated 

 mass of protoplasm containing various nutritive substances (oil, 

 starch, etc.). It generally has a cell-wall, which is commonly 

 thick, and in some cases consists of two layers, an outer, the exine 

 (or exospore], which is cuticularised, and an inner, the inline (or 

 endospore), which is delicate and consists of cellulose. 



In some cases the spore has no cell-wall. It may then be cap- 

 able of spontaneous movement. When motile, it usually swims by 

 means of one, two, four, or many delicate protoplasmic filaments 



