92 



STATE HORTICULTURAL SOCIETY. 



the top of each of which one or more ovate spores are produced. These 

 are the conidia, or summer spores, and are produced in vast quantities for 

 several weeks. 



" Within the perithecia, as 

 winter approaches, may be 

 found great numbers of elon- 

 gated sacs or asci in each of 

 which eight spores are found. 

 They ripen in midwinter or 

 early sj^ring and will germin- 

 ate and develop into a fungus 

 the next summer. 



"Besides the ascospores and 

 conidia, there are several 

 other means of reproduction 

 possessed by this plant. 

 Among them are the stylo- 

 spores, which are developed 

 from the inner walls of cavi- 

 ties located between the pefi- 

 fJiecid. They are on slender 

 stalks and have a coiupound 

 spore in four parts or cells at 

 the end. 



"Spores are also produced 

 in the s^wr mag on in which are 

 organs much like the perithe- 

 cia, but, instead of the asci, 

 •they produce slender fila- 

 ments. 



"Still another form are the 

 jrijoiidia spores, which are 

 pushed out from cavities in 

 soft, wormlike masses. 



"The periilu'cia may be 

 likened to the pistils of flower- 

 ing plants and some of the 

 other organs undoubtedly cor- 

 respond to the stamens. 



"With all those methods 

 of propagation, the black -knot 

 needs but half a chance, to spread devastation through our plum and 

 cherry orchards, and constant watchfulness is necessary to keep it in check 

 if it once gains a foothold. 



"The first thing to be done should be to destroy all the choke-cherries 

 and wild plum trees in the vicinity. The orchards should be examined 

 frequently, during the growing season, and if a knot appears, the branch 

 should be cut ofp several inches below the knot, and burned. Cutting off 

 the knots and leaving them on the ground will do no good, as the spores 

 will develop the same as if on the tree. 



" If the knots are on the trunk, where they cannot be cut out without 

 injury to the tree, they should be pared ofl^ smoothly and the cut surface 

 and surrounding bark painted over with linseed oil. This will destroy any 



Fio. 2.— Black Knot. 



1. Section tlirongh diseased stem, tiln)wing niyceliuin. 



2. Spermaaonia. 



3. Asci and spores. 



4. Perithecium with asci. 

 5 and 6. Ripe Ascosijores. 



7 and 8. Ascospores germinating. Aft«r Farlow. 



