196 



BOTANY 



PART I 



wall, and as a rule able to move through the water by the aid of 

 cilia (Figs. 225, 229 A). They are termed SWARM SPORES or ZOO- 

 SPORES, and the receptacles in which they are formed are spoken of 

 as ZOOSPORANGIA (Green and Brown Algae, some Phycomycetes). 



The spores in other Thallophyta are adapted to dispersal by 

 wind. Examples are afforded by many sporangial spores and all 

 conidiospores of the Fungi. They are very small and light, sur- 

 rounded by thick walls and resistant to drying. Such spores are 

 usually produced by organs which are exposed to the air ; in Fungi 

 living in or on solid substrata 

 they may be borne on aerial 

 hyphae (Fig. 224). They are 

 thus borne on CONIDIOPHORES or 



SPORANGIOPHORES Or On FRUCTI- 

 FICATIONS. 



FIG. 224. Conidiophore of Aspergillus 

 herbariorum. (x 540. After KNY.) 



FIG. 225. Saprolegniamixta. Sporangium from 

 which the biciliate zoospores (s 2 ) are escap- 

 ing. (After G. KLEBS.) 



In the Bryophyta, Pteridophyta, and Spermatophyta the asexual 

 cells are always developed as endospores in special sporangia of more 

 complicated structure than in the Thallophyta. These sporangia are 

 multicellular structures, one or more outer layers of cells forming the 

 wall, and the enclosed cells constituting the sporogenous tissue 

 (Fig. 226 sg). When ripe, the sporangia have usually special arrange- 

 ments in the wall for opening and shedding the small and light 

 spores, which may be dispersed by wind or (in the case of many 

 Spermatophytes) by animals. The spores are always surrounded by 

 cell walls. 



The spore capsules or SPOROGONIA of the Bryophyta attain the 

 most complicated structure. They are as a rule stalked and are 

 situated on the thallus or at the ends of leafy branches. The sporo- 



