294 



FUNGOUS DISEASES OF PLANTS 



The fungus has been isolated and can be readily grown in 

 artificial media. Upon starchy media, or media containing con- 

 siderable sugar, it produces a very vigorous growth, often cottony 

 in appearance. Glucose agar, corn meal, etc., are colored pink, 

 or some shade of deep red after growth of a week or more ; but 

 the color is less intense when the fungus is grown on starchy 

 products, apparently, than on a glucose agar. 



The fungus. It produces two forms of conidia, which have 

 been designated microconidia and macroconidia (Fig. 129). The 

 microconidia are more or less subspherical, or slightly pointed at 

 the base, even pear-shaped, and they are produced by a constric- 

 tion from lateral or 

 terminal branches, the 

 latter being sometimes 

 clustered. Each branch 

 may produce a large 

 number of conidia by 

 successive abscision, 

 and the conidia fre- 

 quently become massed 

 together in balls. They 

 vary from 5.5 to SJJL 

 in diameter, and are 

 capable of immediate 

 germination, producing a much branched mycelium. The macro- 

 conidia are far less frequent in culture and in nature than the 

 microconidia. The method of production of the former type is 

 practically the same as in the case of the microconidia. There is, 

 however, greater vacuolation of the protoplasmic contents during 

 the formation of the macroconidia, which, moreover, may become 

 ovoidal, and finally further elongate, becoming once or more septate. 

 They measure 4.5-5.8 x 10-17.5/4. Owing to the fact that the 

 conidia are in general microconidia, properly the type of the genus 

 Sporotrichum, this fungus is retained in that genus. 



Control. This disease is often one of serious importance in 

 well-arranged and sanitary carnation houses ; but it is apparently 

 most to be feared where conditions for forcing the host are desired, 

 or where unsanitary conditions prevail. Control or prevention 



FIG. 129. SPOROTRICHUM PoAi: CONIDIOPHORES 

 AND CONIDIA 



