140 CYSTOPUS, OR WHITE RUST. 



days, or even weeks after sowing, one examines the epidermis and 

 the tissue beneath, one finds the germs to all appearances fresh, 

 but without having changed the aspect they exhibited on the first 

 day." He asks then, "How are the plants infected?" and 

 answers, " It is only the germs which enter by the stomata of the 

 cotyledons, whose growth produces mycelium." 



They enter in the manner already described ; soon the termi- 

 nal swelling lengthens out, branches, and assumes all the qualities 

 of ordinary mycelium. These first tubes are gifted with the 

 faculty of growing, and branching out to an extent only limited by 

 the hospitable plant ; and if the plant possesses sufficient vitality 

 to live through the winter they live with it and revive their vege- 

 tation in the spring. " I shall not hazard an explanation of these 

 singular facts, because one knows too little about the difference 

 between the composition of the leaves and that of the foliated 

 cotyledons of the Cruciferae. I confine myself to a detailed 

 account of the experiments which gave me the result indicated. 

 All the experiments have been made with plants of Lepidiiim 

 sativum, growing from seeds of the same crop. They were sown 

 in flower-pots, placed in a room, and watered carefully, so that 

 nothing might be touched by the water except the soil. 



" On 29th Oct., fifty-six plants of Lepidimn had just displayed 

 their cotyledons. I pulled up six, and plunged them into water 

 containing a large number of conidial zoospores, and the little 

 plants fell to the bottom of the vase. On 30th Oct., the epidermis 

 of three of them was examined microscopically, and showed a great 

 number of germs penetrated into the stomata ; the three others 

 were planted in the ground, and continued to grow. On Nov. 2nd 

 the cotyledons of one of them were examined ; they contained 

 very fine tubes of branched mycelium growing from the germs 

 which had entered by the stomata. On Nov. 17th, the cotyledons 

 of the two remaining plants were drooping, and conidial swellings 

 were visible on both surfaces. On Dec. 21st, each of the plants 

 displayed their first two leaves, which were covered with pustules 

 of Cystopiis, and at the end of December the plants died. Five of 

 the original fifty-six plants, planted separately, received on their 

 cotyledons drops of water charged with zoospores. Within a 

 month all of them had developed Cystopus, and a fortnight later 



