CHAPTER IV. — INTRODUCTION. 1 29 



gonidia ; Tulasne reserves the word spore in many Fungi for certain special forms 

 of them, and uses a different word for all others. Sachs' practice is intelligible and 

 precise 1 ; he sets out from a consideration of the Ferns and Mosses, and reserves 

 the word spore for the cells produced in the sporophyte or sporocarp and for their 

 homologues in other plants, while for all such as are not homologous with them he 

 uses the words gonidia, brood-cells, or some similar term. This plan may be easily 

 carried out in the very distinct and comparatively limited domain of Ferns and Mosses, 

 even if the formation of free propagative cells other than spores were not reduced in 

 these plants to the very smallest possible amount. For the whole field of botany it is 

 correct but impracticable because the homologies of many free reproductive cells in 

 the lower Thallophytes are still unknown, and we are still in want of. a satisfactory 

 general expression to denote a distinct and evident phenomenon. 



To meet this need we here conform to the vox popidi and apply the term spore 

 quite generally to every single cell which becomes free and is capable of developing 

 directly into a new bion, without regard to genesis and homology. This definition 

 excludes from the conception of a spore all oospheres and gametes which require 

 fertilisation or conjugation, and all cells directly endowed with the male sexual 

 function. The forms that come under the definition may for convenience sake be 

 distinguished either by compounds of the word spore or by some special terms, and 

 these may continue to be simply opposed to the word spore, where this is possible, 

 as in Ferns and Mosses. The discrimination of spores will depend on different 

 relationships, according to which the same spore may receive different names, as 

 happens in all other things. For example we should distinguish — 



1. According to sexual relations : 



a. spores which are developed from sexually fertilised oospheres, oospores 



as Pringsheim happily termed them ; or the product of conjugation of 

 two similar gametes, zygospores. 



b. spores not sexually developed. 



2. According to structure : swarm-spores and spores that do not swarm (see 

 above in Chapter III) and many special forms. 



3. According to position in the course of development, homology : in many 

 of the Hepaticae, Scapania nemorosa for example, we must distinguish between 

 the carpospores (spores simply) which are produced in the fructification and the 

 structures formed on the leaves and usually termed brood-cells or gonidia, and we 

 may extend these expressions to all members of the vegetable kingdom which show 

 the rhythm of development of the main series. Carpospores would thus be the 

 spores which represent the stage of the development proceeding directly out of the 

 archicarp or typically concluding its further development, such as the oospores of 

 the Algae, the ' spores ' of Mosses and Ferns, the carpospores of the Florideae ; 

 gonidia would be all other spores, as the tetraspores of the Florideae, most of the 

 swarmspores of the Algae, the spores of many of the Fungi which are the homo- 

 logues of these swarmspores and will be described in succeeding chapters ; for these 

 latter forms the term conidia introduced by Fries is in general use. 



4. According to the mode of development : thus in the Fungi we have 

 ascospores (i/iccaspores), acrospores, &c. 



1 Lehrbuch, Aufl. 4. 



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