292 BOTANY. 



a sexual process precede the formation of each receptacle 

 which springs from the sclerotium. It may be, however, 

 that each perithecium is the result of a sexual act ; in the 

 latter case the single perithecium would be the homologue of 

 the Peziza cup, while in the former the whole receptacle of 

 Claviceps would be homologous to the receptacle of Peziza. 



386. As a second illustration of the plants of this order, 

 the Black Knot (Sphceria morbosa) which attacks the plum 

 and cherry may be taken.* In the spring the hyphae, which 

 the previous year penetrated the young bark, multiply 

 greatly, and finally break through the bark, and "form a 

 dense pseudo-parenchymatous tissue." The knot-like mass 

 grows rapidly, and when full sized is usually from two or 

 three to ten or fifteen centimetres long ( 8 or 1.2 to 4. or 6. 

 in.), and from one to three centimetres in thickness (.4 to 

 1.2 in.) ; it is solid and but slightly yielding, and is composed 

 of hyphae intermingled with an abnormal development of the 

 phloem parenchyma of the host plant ; bast fibres and modi- 

 fied vessels of the wood also occur. Externally the knot is 

 at this stage of a "very dark brownish-green color," and has 

 a velvety appearance, Avhich is due to the fact that its surface 

 is covered with myriads of short, jointed, vertical hyphae, 

 each of which bears one, two, or more ovate pointed conidia 

 (Fig. 200, 1). The conidia fall off readily, and doubtless are 

 important agents in multiplying the number of these para- 

 sitic growths ; they are produced until the latter part of 

 summer, when the hypha branches which bear them shrivel 

 up and disappear. 



387. During the latter part of summer perithecia are 

 produced ; but the asci require the greater part of winter to 

 come to perfection. In February the ascospores are fully 

 ripe. The perithecia at this time are nearly globular in 

 shape, and are situated in minute papillae (3, Fig. 200) ; the 

 asci loosely cover the walls of the perithecial cavity, and are 

 intermingled with slender paraph yses (4, Fig. 200). Each 



* What follows is condensed from a paper on " The Black Knot," by 

 Professor W. G. Farlow, in the Bulletin of the Bussey Institution, Vol. 

 I., p. 440 (1876). Three excellent plates accompany the paper. 



