SECT. m. UREDO. 279 



variable extent. The summit of ea^h of these club- 

 shaped tubes is formed into a conidium, or spore dust 

 cell, which separates itself from that below it by taking 

 a globular form. In the upper end of the remainder of 

 the tubes, new spore dust cells are formed, and so on 

 indefinitely. These conidia remain attached to one 

 another in a string by slender constrictions which 

 become thinner, and at last give way from above down- 

 wards, and they escape in succession through a crack 

 in the skin of the leaf. The quantity of spores that 

 are generated by the dense mass of these club-shaped 

 tubes must be enormous. 



The Cystopus has female reproductive cells, which 

 had escaped notice from being hid in the plastic matter 

 which nourishes them. They appear before the spore 

 dust bearing cells, and are formed by terminal or inter- 

 stitial swellings in the tubes of the mycelium, which 

 become large oval cells, separated ultimately by a closure 

 from the rest of the tube that bears them; they are 

 filled with a granular liquid mixed with large granules 

 of a coloured fatty matter. The tips of some branches 

 of the mycelium swell into oval or club-shaped cells 

 containing spermatozoids, which fertilize the female 

 cells ; then the matter within the latter assumes a glo- 

 bular form, gets a coat of cellulose, and becomes the 

 true fruit of the Cystopus. 



As early as the year 1807, M. B. Prevost had seen 

 that the sporangia, or spore cells of the entophytes 

 produced zoospores, and recently M. de Bary has seen 

 them produced, during the germination of the spores, 

 collected within a sporangium of the Cystopus. When 

 they came into the water they had two cilia, one of 

 which was short and went first, the other was long and 

 trailed after the zoospore. Neither M. de Bary nor M. 

 Tulasne have ever seen zoospores in the fungus itself, but 

 if the drops of rain or dew round the white spot on the 



