DAMPING OFF FUXGUS AND ALLIED FORMS. 231 



■deony, and tliat the root-hairs are destro3^e(l. J.ater, if the plant 

 is not vigorous enough to resist the fungus and to put forth 

 seeoiuhiry roots, the disorganization of tissue extends to the stem, 

 resulting ultimately in the toppling over of the plant and its 

 thorough decay, although in some instances the plant remains 

 green for several days after falling. This extends from one plant 

 to another until onl}' a few or none of the seedlings in a bed may 

 be left. From the nature of the growth and method of attack of 

 the parasite, it will be seen that it is naturally more fatal to deli- 

 •cate seedlings and those which get their growth slowly than to 

 others. Such plants as Gilia, Viscaria, Lobelia, etc, are much 

 more likely to be injured than more robust forms. The conditions 

 ^hich are most favorable to its growth are moist atmosphere, high 

 temperature, Avith shade, or cloudy weather. 



At the suggestion of Professor W. G. FarloAv, upon the 

 appearance of the disease at the Botanic Garden of Harvard 

 College, I undertook to ascertain the exact botanical character of 

 the cause, or causes, of damping off. I soon became convinced 

 that the conjecture which had been offered, — that a Pythium was 

 the real parasite, — was correct. The features above given being 

 accepted as characteristic of the malady, many seedlings so 

 affected were examined. The tissues of such plante, especially in 

 the roots and in the stem just above the surface of the ground, 

 are readih" seen to be permeated by the hypha? and reproductive 

 bodies of a species of Pythium. The- same fungus was found in 

 considerable abundance running over the sand, and in the dead 

 leaves of Sphagnum which covered portions of the bed. I col- 

 lected some of the Pythium from the moss and sand, — because 

 there it could be obtained more free from bacteria and hyphomj^- 

 cetes than in the tissues of the living plant, — and sowed it upon 

 tender bits of plant tissue placed in Van Tiegham cells, in a 

 hanging-drop culture. By transplanting from cell to cell, I 

 secured Pythium as free as possible from other forms of fungi. 

 This, while growing freely and under the most favorable artificial 

 conditions which could be secured, was sown upon seedlings of 

 Gilia tricolor Avhich had been germinated and grown in sterilized 

 earth, and which had shown no signs of damping off. Within 

 five days after the addition of the Pythium, seventeen plants out 

 of twenty-three had been attacked by it, and fourteen of these 



