REPRODUCTION. 603 



peculiarity in this mode of their origin, to indicate the order 

 of their development, to assign them without periphrasis to a 

 particular group of plants, etc. Thus, as has been already 

 mentioned, zoospores are motile spores : stylospores are spores 

 which are developed, not in sporangia, but by abstriction 

 as described above: tetraspores is the name given to the 

 asexually produced spores of the Florideae to denote the fact 

 that usually four spores are produced by the division of the 

 mother-cell : the uredospores of the Uredineae are those which 

 are produced during the summer, whereas the teleutospores of 

 these Fungi are those which are formed in the autumn at the 

 close of the season of growth. The spores of the Fungi are 

 sometimes spoken of generally as conidia, and the word gonidia 

 is sometimes applied to the spores of the Algae. Certain vas- 

 cular plants, constituting the Rhizocarpae (Hydropterideae), 

 the Ligulatae, and the Phanerogams, produce spores of two 

 kinds, and are therefore said to be heterosporotis, therein 

 differing from their allies the Ferns, Equisetums, and Lyco- 

 podiums, which produce spores of one kind only, and are 

 therefore said to be isosporous or homosporous. The two kinds 

 of spores differ in size, and also in that they give rise to 

 different organisms on germination. On account of their 

 difference in size they are distinguished as large spores or 

 macrospores and small spores or microspores, and the organs 

 producing them are termed respectively macrosporangia and 

 microsporangia. In the Phanerogams these organs are more 

 familiarly known by other names; in this group of plants 

 the macrosporangium is termed the ovule, and the macro- 

 spore, the embryo-sac ; the microsporangium the pollen-sac, 

 and the microspore, the pollen-grain. In some of these plants 

 there is the further peculiarity that the spore is not liberated 

 from the sporangium, but germinates there: this is the case 

 with regard to the microspores of Salvinia among the Rhizo- 

 carpae, and with regard to the macrospores (embryo-sacs) of 

 the Phanerogams. This peculiarity in the Phanerogams, 

 leads, as we shall subsequently learn more fully, to the pro- 

 duction of that structure, the seed, which is characteristic of 

 these plants. The production of a seed constitutes, in fact, 



