EVOLUTION OF PARASITIC FUNGI. 105 



ozonium, for example, or the rhizomorphs which are connected 

 with the Agariciis melleus. 



There is no doubt a tendency in a vast number of species to 

 eliminate, or to become permanently separated from, some one- 

 time complemental form. Many of these are represented in the 

 so-called " imperfect fungi," and one or more of our common 

 species of Botrijtis at least exhibit a tendency in this direction, 

 if they have not already become permanently divorced from the 

 complemental peziza form. One of these, Botri/tis vvlgaris, is 

 especially abundant in forcing houses, attacking nearly all kinds 

 of plants, and growing indifferently as a saprophyte or as a 

 parasite, though perhaps more fre(iuently as the former. It is 

 well known by its conspicuous fuzzy growth on the surface of 

 the affected parts of the plants as it matures its conidia. The 

 mycelium, which is profusely branched and septate, grows in the 

 tissues of the attacked plants, penetrating the cell walls and 

 causing a soft rot of the tissue. From this mycelium the erect 

 conidiophores, or fruiting threads, arise through the epidermis, 

 and at a little distance from the surface produce quite a number 

 of short divergent branches, which bear near the ends oval 

 conidia in svxch a crowded condition that they appear to form 

 small heads. At first this fuzzy growth is colorless, but with age 

 it becomes grayish-white or grajnsh-brown in color. Besides the 

 peculiar grappling organs which it develops, and which are said 

 to excrete a ferment that dissolves the cellulose of the host plant 

 at the point of attack, and thus to aid the fungus in gaining an 

 entrance to the tissues, there are developed in artificial cultures, 

 on suitable media, numerous black sclerotia composed of com- 

 pactly interwoven fungus threads. 



I have on repeated occasions seen these develop, especially on 

 sterilized bean stems, or other sterilized plant tissue, in great 

 numbers. Several times an attempt has been made to grow a 

 perfect form from the sclerotia, but always with negative results 

 up to the present time. The sclerotia probably need a period of 

 rest, and this period has been given for several months on differ- 

 ent occasions, and when the sclerotia were planted on moist sand 

 they invariably developed the well-known conidiophores of the 

 botrytis form which appear on the diseased plants. Perhaps 

 the period of rest for the sclerotia has not been sufiiciently pro- 

 longed. I have sclerotia now which are more than one year old, 



