REPRODUCTION. 635 



their appearance. The sexually produced spore (aecidiospore) 

 gives rise to an individual which, in Gymnosporangium and 

 Hemipuccinia, bears asexually produced spores, teleutospores 

 (p. 603) ; in Puccinia Graminis the formation of teleutospores 

 is preceded by that of somewhat different spores, the uredo- 

 spores; in either case the teleutospore gives rise to a second 

 asexual generation, the promycelium, which bears sporidia, 

 from which the aecidium-bearing oophore is developed. 



We may, in conclusion, briefly consider the relation of 

 vegetative reproduction to the life-history of plants. It has 

 been stated that in the life-history of a plant which exhibits 

 regular alternation of generations, the alternate generations 

 are developed from spores produced either sexually or asexu- 

 ally as the case may be. But to this there are exceptions, for, 

 as we have already learned (p. 60 1), reproduction by means of 

 spores may be replaced by vegetative reproduction, in the 

 form either of apogamy or of apospory. Thus in the vege- 

 tatively apogamous Ferns already mentioned, the sporophore 

 (fern-plant) is developed as a bud upon the oophore (pro- 

 thallium). Similarly in the aposporous Ferns, Mosses, and 

 Characeae, the oophore is developed as a bud from the 

 sporophore. 



In some cases, namely when one generation gives rise 

 to its like by vegetative budding, sporophore to sporophore, 

 oophore to oophore, there is a combination of vegetative 

 apogamy and apospory. For instance, when as in the Phane- 

 rogams mentioned above (p. 60 1), embryos are produced vege- 

 tatively from the tissue of the nucellus, sporophore springs from 

 sporophore, the normally intervening formation of spores, first, 

 by the asexual method, and secondly, by the sexual method, 

 is suppressed. A striking instance of the same thing has 

 been observed by Goebel in some species of Isoetes in which 

 a plant was developed on a leaf in place of a sporangium. 

 Other instances are afforded by the various cases of multi- 

 plication by buds referred to at the beginning of this lecture 

 (p. 601). Similarly, when a moss-plant gives rise by budding 

 or by means of gemmae to another moss-plant, or when a 

 fern-prothallium gives rise to another by means of gemmae, 



