INTRODUCTION. 



^^33 



I 



^^Hporangia of Ferns and capsules of Mosses. These are obviously the result of a 

 vegetative process, excited by the act of sexual union, in consequence of which 

 they arise on the second (non-sexual) generation [sporophore] which springs from 

 l^^be fertilised oosphere of the first (sexual) generation [oophore]. Let us now 

 ^^^ansfer these conceptions to the most highly developed Thallophytes which ex- 

 hibit an evident alternation of generations, as the Ascomycetes. We have already 

 n, in the Section referred to, that the ascospores of Penicillium are the result 

 a vegetative process brought into action by the sexual organs of the mycelium, 

 d which has for its result the formation of the tuberous fructification which 

 nstitutes the second generation. The ascospores of Penicillium therefore cor- 

 pond to the spores of a Moss or a Fern. If now we suppose the result of 

 ;e union of the sexual organs to be a very inconsiderable vegetative structure, 

 d the second generation consequently to be merely rudimentary and a simple 

 pendage to the first, the spores themselves would then seem to be an almost 

 immediate result of fertilisation, as occurs for instance in the Nemaliese (Fig. 164, 

 C, p. 237). If we were further to imagine that the act of fertilisation did not 

 result in the production of any vegetative structure, or the second generation to 

 be altogether suppressed, the fertilised oosphere would then itself become a spore, 

 as in the Coleochaetese, (Edogonieae, and Vaucheria. In this case the spore is 

 an equivalent for the whole of the second generation ; it stands for the entire 

 fructification of the Ascomycetes, the entire spore-capsule of a Moss, «&c. Precisely 

 the same is true for the zygospore which results from conjugation. The zygospore 

 (as for example in the Mucorini), or the oospore (as in Vaucheria), represents there- 

 fore in a morphological sense the entire second generation of these plants. This 

 conclusion, which might easily be proved more in detail, may be briefly summed up 

 in the statement that the Spore is either an immediate product of fertilisation 

 (zygospore, oospore), or of a process of growth which is induced by fertilisation ; and 

 this vegetative growth may either be inconsiderable, as in the Nemalieae and Erysiphese, 

 or it may be considerable, and it then gives rise to the second generation in which 

 the spores are produced, as in Penicillium and other Ascomycetes. This explanation 

 shows at once how in Thallophytes the second generation is a gradually increasing 

 structure developed in consequence of the act of fertilisation. But for the purpose 

 of a scientific nomenclature the term Spore (if used in the same sense as in 

 Muscineae and Vascular Cryptogams) must be applied in Thallophytes only to 

 those reproductive cells which are the result of an act of impregnation, whether 

 direct, or indirect through the production of a vegetative body which constitutes 

 a second generation and closes the entire course of development of the plant. All 

 other unicellular and non-sexual organs of reproduction we shall not term spores, 

 but gonidia or cojiidia. 



We may now proceed to a further description of the various kinds of sexual 

 organs found among Thallophytes, and of the true spores which result from their 

 union with or without an alternation of generations. The following three principal 

 forms or types may be distinguished \ 



* More minute evidence of the statements here made will be found in the sequel in the 

 description of Algae and Fungi. The facts stated are derived from the writings of Pringsheim, 



