ROSE CANKER AND ITS CONTROL. 



15 



Fig. 4. — Tuft of conidiophores 

 on a dead rose stem. 



CONIDIOPHORES. 



The conidia, or ordinary spores, — as distinguished from the chlam- 

 ydospores, — are borne on special upright branches, — conidiophores. 

 These are produced in great abundance in artificial culture, but are 

 rarely seen on the cankers. The writer has found them occasionally just 

 at the surface of the ground on young shoots 

 recently killed by the pathogene. But in 

 badly infested rose beds which are kept wet 

 they are produced in great abundance on 

 dead shoots and parts of the rose plants 

 which are cut off and left to decay on the 

 ground under the bushes. To the naked eye 

 the dead shoots seem to be dusted over in 

 patches with a white powder. Under a 

 strong hand lens — or better, a binocular 

 microscope — each particle of this white 

 powder is seen to be composed of a tuft of 



slender-stalked "brooms" with glistening white heads. One of these 

 tufts is shown in Fig. 4. Each httle broom is a conidiophore with its 

 mass of conidia on the apex. The number of conidiophores in a tuft 

 varies from 5 to 40, or more. No de- 

 tails, further than shown by Fig. 4, can 

 be made out 

 under the bin- 

 oculars. Under 

 the compound 

 microscope, 

 however, it is 

 possible to de- 

 termine accu- 

 rately the struc- 

 ture of these 

 little brooms. 

 Examined in 

 the dry condi- 

 tion they ap- 

 pear as in Fig. 

 5, where the 

 conidia are 

 cemented to- 

 gether into a solid head. But when mounted in water the cement 

 which holds them together dissolves, many of them float away, and 

 the head becomes loose as represented in Fig. 6. The main stem of the 

 conidiophore may be unbranched up to just below the conidia, as repre- 

 sented by Fig. 5, or it may show one or more monopodial branches at 



Fig. 5. — Conidiophores and 

 conidia as seen in a dry 

 condition. 



Fig. 6. — Conidiopliores as seen when 

 mounted in water, many of the conidia 

 washed away. 



