VERTICIUJUM HF/TEROCLADUM. 



23 



repentibus, elongatis, paulltim ramosis, continuis; ramis fertilibus adscendentibus, 

 ramnlosis ; ramulis ternis vel quaternis, oppositis vel alternis, patentibus, rectis, apice 

 attenuatis ; conidiis in ramulorum apice solitariis, geminatis vel ternis, saepius pedi- 

 cellis brevissimis stiff ultis, oblongis, hyalinis, 5.5-6 micr. long., 2-3 micrTcfassis. 



Verticillium heterocladum, in general 

 appearance, resembles the Brown fungus 

 of Webber (Plate IV, Fig. 31). On close 

 examination, however, it is found to be 

 strikingly different. The pustules, which 

 are cinnamon colored, are powdery on 

 the surface. Under the hand lens, they ap- 

 pear brushlike in form, bristling with 

 hyphae. From the edge of the pustules 

 there grows out a creeping layer of white, 

 delicate, interwoven hyphae. From these 

 colorless hyphae, as well as from the top 

 of the pustules, there arise upright con- 

 idiophores. These may have eithet a 

 simple series of whorls, 2 to 4 branches 

 in each, or the branches of the whorls 

 may again be whorled. The conidia are 

 borne on the ends of the ultimate 

 branches (Fig. 10). 



The conidiophores are quite delicate, 

 slender, hyaline, 150 to 240 microns by 

 times septate. The conidia are oblong, hyaline, 

 The main body of the cinnamon- 

 in 



Fig. 10. Verticillium hetei-ocladum. () Conidio- 

 phore with conidia forming, X 450. (b) 

 Conidiophorewith mature conidia. X 450. 

 (c) Conidia, X 1000. 



o to 4 microns, several 

 4 to 6 microns long by 1.5 to 2.5 thick, 

 colored stroma when mature becomes powdery 

 appearance, and under the microscope it is found 

 that the hyphae have broken up into short pieces 

 irregular in shape and length with rounded ends, 

 some of them quite closely imitating spores (Fig. 

 11). These have thicker walls than the conidia, 

 and probably act as reproductive bodies in carry- 

 ing the fungus through a period of dry weather. 



Fig. 11. Short hyphal bodies 

 into which the central por- 

 tion of a mature pustule 

 breaks up, X 450. 



CULTURES. 



Pure cultures of this fungus were made in November, 1905, soon after 

 the fungus was discovered on Aleyrodes citri. The next year other cultures 

 were made and spores of the fungus transferred from cultures to larvae 

 of Aleyrodes citri in the greenhouse. The fungus was readily grown in 5 

 per cent, glucose agar by drawing a moistened platinum needle over the 

 top of the upright conidiophores and then washing it off into the melted 

 agar. 



On November 12, 1906, two petri dishes (A and B) of 5 per cent, glu- 



