SPORE-WALL PORES 



545 



two which have uniporous uredospores, namely, Uromyces uniporulus 

 and Puccinia monopora} The several pores of a single uredospore, 

 e.g. of Puccinia graminis and P. dispersa, are always arranged on 

 the walls at some distance apart. 



The aecidiospore of most Uredineae, according to Sydow, Grove, 

 and others, has numerous indistinct pores or often possibly none 

 at all. 2 



In considering the significance of the position and number of 

 the pores in teleutospores, uredospores, and aecidiospores, the 

 function of the pores 

 as germ-pores must be 

 borne in mind. Since 

 the pores of aecidio- 

 spores are so indistinct 

 and since relatively 

 little is known about 

 them, we shall exclude 

 aecidiospores from the 

 following remarks and 

 confine our attention 

 to uredospores and 

 teleutospores. 



Why should a uredo- 

 spore have several 

 pores in its wall ? I believe the answer is : to provide that at 

 least one pore shall be on the side of the spore which happens 

 to be turned towards the epidermis of the host-plant, and thus 

 to assist the process of germination. Uredospores and pollen 

 grains are analogous in the provision of, and functioning of, their 

 pores. In the pollen grains of most Phanerogams, as in uredo- 

 spores, there are several pores scattered upon the walls. Thus 

 in Colchicum autumnale there are 2 pores ; in most species, e.g. 

 the Fire-weed, Willow-herb, Nettle, Oak, and Hazel, 3 pores ; 

 in the Alder and Birch 4 to 6 pores ; in the Currant 8 to 

 12 pores ; in the Convolvulus 15 to 18 pores ; in the Carnation 

 and Mezereon 20 to 30 pores ; and in Nyctagineae over 30 

 1 W. B. Grove, loc. cit., p. 33. 2 /^^^^ p gj 



VOL. III. 2 N 



Fig. 221. — Hyalopsora Aspidiotus. To show pores 

 in the walls of the uredospores. To the left, 

 part of a frond of Polypodium Dryopteris, 

 showing uredo-sori, natural size. To the right, 

 three uredospores, all from the same sorus, 

 the central one with 4 pores, the right-hand 

 one with 6 pores, and the left-hand one with 

 7 pores, magnification 600. Material from 

 Scotland. The faint, hardly perceptible warts 

 on the exterior of the walls of the aecidiospores 

 are not shown. From W. B. Grove's British 

 Rust Fungi. 



