Pomona College Journal of Economic Botany. 



321 



The method by which the fungus obtains entrance into the plant stem 

 has not been entirely determined, but it doubtless gains entrance through a 

 wound or by first establishing itself upon dead or inactive tissue and then 

 penetrating the living tissue. At every stage in the growth of the carna- 

 tion there is more or less idle tissue upon it. The cutting in starting its 

 growth develops new leaves from the center, the outer ones remain green 

 for a time and finally die. These outer leaves, if at all moist, afford an 

 excellent means for the entrance of the fungus into the inner tender tissues 

 of the plant. The carnation stem frequently checks, thus forming easy pas- 

 sageways to its interior and deadened areas formed on the margins of the 

 checks may give the fungus a foothold. When the flowers are cut they 

 are not necessarily cut at a node, and if they are not the portion of the 

 stem extending beyond tlie node dies; in fact, such a stem often dies back 

 to a main branch. All of these dead parts and bruises afford an opportu- 

 nity for the disease organism to enter the plant. The fungus is undoubt- 

 edly parasitic under favorable conditions. 



Stems of diseased carnation plants placed in moist chambers rapidly 

 develop tufts of mycelium on their surfaces which originate from filaments 

 which have broken through the epidermis of the stem or from clusters of 

 spores formed on the outside of the stem. These tufts of mycelium are 

 5-10 mm. high, usually white, but sometimes they are pink or yellow in 

 color. Macroconidia develop in them, and a pure culture could be easily 

 obtained by simply touching one of these tufts with a sterile platinum 

 needle and transferring the spores to a poured plate. 



DESCRIPTION OF THE FUNGUS 



The mycelium found in diseased plants is colorless, slightly more slen- 

 der than that grown in cultures, much branched in the parenchyma and 

 with frequent septa. The septa are 5 u. to 10 u. apart and the mycelium 

 varies in width from 3.5 u. to 6 u. No microconidia have ever been found, 

 either borne within the host, or developed in cultures. The fungus was 

 obtained in pure cultures from three different sources: Alameda, Rich- 

 mond, and Elmhurst. One strain was established from a single spore, this 

 spore was taken from the Elmhurst culture. A careful study of each 

 strain was made in drop cultures of beef extract bouillon (Ml). The Van 

 Tieghem cell was u.sed for these studies. The macroconidia germinated in 

 less than twenty-four hours; some germinated from the end cells and some 

 from the central cells of the spore (Plate V, Figures 6 and 7). In forty- 

 eight hours quite a profuse mycelium had formed, and it had grown across 

 drops two and three millimeters in diameter. At the end of seven days 

 the formation of macroconidia began; these were the only variety of spores 

 developed in drop cultures. They were formed inOvSt rapidly in places 

 where the mycelium came in contact with the glass outside of the drop ; 

 such contact seemed to stimulate the formation of spores. The macroconidia 



