370 



THALLOPHYTES 



velvety appearance. These erect hyphae are conidiophores and 

 bear conidiospores as shown at B in Figure 320. The conidi- 

 ospores are scattered by the wind and upon germination grow 

 directly into hyphae which can penetrate a young shoot and start 



the disease anew. In late 

 summer after the produc- 

 tion of conidiospores is 

 over, the knot becomes 

 black and on its surface 

 occur numerous small 

 papillae which are the 

 flask - shaped perithecia, 

 opening with a pore and 

 lined on the inside with 

 asci as shown at C n 

 Figure 320. The asco- 

 spores are mature and 

 ready to be distributed 

 early the next spring. 



It follows then that the 

 disease may be spread dur- 

 ing the early spring by 

 ascospores or during late 

 spring and summer by the 

 conidiospores. The de- 

 struction of the knots be- 

 fore the shedding of the 



D 



FIG. 320. Black Knot, Plowrightia 

 morbosa. A, branch of a Plum, showing the 

 wart-like excrescences caused by the Fungus; 

 B, conidiophores producing conidiospores 

 (X 500), and at the right a conidiospore 

 germinating; C, two perithecia sectioned 

 lengthwise, showing the asci and paraphyses 

 within ( X 50) ; D, asci and paraphyses more 

 highly magnified. 



spores will check the dis- 

 ease. Bordeaux mixture 

 applied at proper times is 

 useful in checking the dis- 

 ease, but most attention 

 should be given to the de- 

 struction of the diseased 



branches. 



Ergot (Claviceps purpurea and Paspali). 1 Ergot is a parasite 

 on the young ovaries of the Grasses, being especially common on 

 Rye and occurring sometimes on Wheat, Barley, and a number of 



1 Ergot and Ergotism. Press Bulletin 23, Nebraska Agr. Exp. Sta., 1906. 

 Life History and Poisonous Properties of Claviceps Paspali. Vol. 7, No. 9, 

 pp. 401-406, Jour. Agr. Research, U. S. Dept. Agr., 1916. 



i 



