602 LECTURE XXII. 



reproductive organs. In this case there is. a substitution 

 of vegetative reproduction for reproduction by means of a 

 sexually produced spore, a substitution which is a case of 

 what is termed vegetative apogamy. 



The asexual production of spores is common to nearly all 

 families of plants. In the simplest case of spore-production, 

 of which plants of low organisation, such as Nostoc and 

 Bacillus, afford examples, the spore is formed from the 

 entire protoplasm of a single cell of the plant, which surrounds 

 itself with the characteristic thick cell-wall. In other plants, 

 somewhat more highly organised in this respect, the proto- 

 plasm of a cell, not specially modified but which may be 

 regarded as a rudimentary sporangium, undergoes division, 

 each portion constituting a spore. Examples of this are 

 afforded, among unicellular plants, by Yeast and Protococcus, 

 and in multicellular plants by the Confervoideae, the Ulvaceae 

 and some Florideae. In still more highly organised plants 

 special organs are differentiated for the production of spores, 

 and in the majority of these plants the special organ is 

 a sporangium, that is a capsule in the interior of which 

 the spores are developed. In the Fungi, however (e.g. some 

 Mucorini such as Chaetocladium, the Ustilagineae, the Ento- 

 mophthoreae, the Peronosporeae, the Ascomycetes, the Ure- 

 dineae, the Basidiomycetes), the spores are produced by ab- 

 striction from hyphae which are termed variously conidiophores 

 or basidia. 



As instances of plants in which the asexual production of spores either 

 does not take place or is rare, the following may be mentioned : 



Algce: Zygnemeas, Desmidieae, Fucacese, Characeas, some Florideae 

 (e.g. Lemaneaceae). 



Fungi: Peronosporea ; Pythium vexans, Artotrogus. 



Saprolegniece ; Ancylistes Closterii, Aplanes Braunii. 

 Ascomycetes ; Ascobolus furftiraceus, Pyronema (Peziza) con- 

 fluens, Gymnoascus, Eremascus, Sordaria (Hy- 

 pocopra), Collemaceae and other Lichen-fungi. 



In many cases, in speaking of asexually produced spores, 

 a prefix is added to the word "spore," or an altogether 

 different term may be employed, in order to mark some 



