DEVELOPMENT OF PLANTS 



255 



the season's growth. These spores, called tc'H(jsi)orc's, arc resting 

 spores and tide the fungus over tlie winter. Furthermore these 

 spores are uninucleate. The two nuclei which have character- 

 ized all cells from the aecial stage on, actually fuse, forminj^^ one 

 nucleus as the teliospores mature. Some regard this as a dchiNed 

 fertilization. The teliospores germinate in the sj)riHg (juite 



}fifi:| 



Fig. 163. Fig. 164. 



Fig. 163. The summer and fall stages of a rust, Puccinia: A, rust blotches 

 on leaf of wheat. B, portion of leaf magnified, showing rupturing of the 

 epidermis due to the formation of spores. C, urediniospores or the summer 

 spores which effect a rapid distribution of the parasite during the summer. 

 D, teliospores or fall spores which are dormant during the winter. 



Fig. 164. Germination of uredinio- and tclio-spores: A, the thin-wallcd 

 urediniospore sending out hyphae from thin places in its wall. This is ef- 

 fected as soon as it is carried by the wind to a moist leaf. 13, teliosporc ger- 

 minating in the spring and forming a short hypha, from the end i>f whirh four 

 cells have been cut off that are forming the basidiospores, b. 



independent of any plant and being deixMideut wyxm llu- lood 

 stored in the spore, they only form short hyphae which usually 

 become divided into four cells (Fig. 164, B). This structure is 

 known as the basidium. Each cell of the basidiuin sends out a 

 delicate tube into the end of which the cell contents passes, thus 



