VIII] 



UREDINALES 



199 



Fig. 169. Gymnosporan^tt-m clavariaefornie 

 Rees; development of spermatia, x 1 185 ; 

 after Blackman. 



simpler forms, such as Phragmidium, the spermogonium is indefinite in 

 extent, and consists of spermatial hyphae arranged beneath the cuticle, which 

 is perforated in the centre of the mass to form an ostiole. No regular para- 

 physes are produced but a few spermatial hyphae may elongate and project 

 as sterile threads (fig. 168 a). 



The spermatial hypha is a long, narrow cell with a central elongated 

 nucleus. It is furnished at its free end with a ring of thickening which may 

 be concerned with the disjunction of the 

 spermatium. The development of the 

 latter begins by the pushing out of a 

 finger-like projection at the apex of the 

 parent hypha. When it has attained its 

 full size the nucleus of the hypha divides 

 and one of the daughter nuclei enters the 

 spermatium, which is cut off by a wall 

 formed just above the thickened ring 

 (fig. 169). 



The mature spermatium is a small 

 more or less oval cell, enclosed in a very 

 thin wall. The cytoplasm is finely 

 granular with apparently no reserve 

 material, and the nucleus is of relatively large size. When cultivated in 

 solution of sugar or honey, spermatia have been induced to undergo a form 

 of yeast-like budding, and this has been observed under natural conditions 

 by Robinson in Pticcinia Poarum. But, though many attempts have been 

 made, it has so far proved impossible to bring about the formation of a 

 mycelium. It seems, therefore, pretty clear that the spermatia are useless 

 as agents of infection, and they differ also in structure from ordinary asexual 

 spores. On the other hand the suggestion was long ago made that they 

 may be male reproductive elements, and this is borne out by their large 

 nuclei and lack of reserve material, and is by no means invalidated by the 

 fact that they possess some slight power of germination. Recent investigation 

 has shown that they are now no longer functional. 



As a rule considerable numbers of spermatia are to be found in various 

 stages of degeneration scattered around the ostioles of the spermogonia. 

 In some cases the spermatia are aggregated in sticky masses and appear 

 to attract insects. The presence of sugars in the spermogonial contents has 

 been demonstrated for species of Uromyces, Puccinia, Endophyllum, and 

 Gymnosporangmm ; in some cases the spermogonia also possess a strong 

 odour as in Puccinia suaveolens, or occur on bright spots which contrast 

 with the green of the surrounding tissue. Such spots are usually yellow or 

 orange, but are white in Uromyces Fabae and reddish-purple in Puccinia 



