CHAPTER IV.—INTRODUCTION. 129 
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’; 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 populi 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. 
d. 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 drood-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 cozıdia introduced by Fries is in general use. 
4. According to the mode of development: thus in the Fungi we have 
ascospores (thecaspores), acrospores, &c. 
1 Lehrbuch, Aufl. 4. 
[4] K 

