CARPOPHYTA. 181 



ments, and their spore-fruits, which are simple or com- 

 pound, are usually hard and somewhat coriaceous. Of the 

 eight families all are ordinary fungi excepting one in which 

 the species are ' ' Lichen "-forming. 



328. A good illustration of the plants of this order is 

 the Black Knot (Plowrightia morbosa), which attacks the 

 plum and cherry. In the spring the parasitic filaments, 

 which the previous year penetrated the young bark, mul- 

 tiply greatly, and finally break through the bark, and form 

 a dense 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 filaments 

 intermingled with an abnormal development of the bark- 

 tissues of the host-plant. 



329. The knot at this time is dark-colored, and has a 

 velvety appearance, which is due to the fact that its sur- 

 face is covered with myriads of short, jointed, vertical fila- 

 ments, each of which bears one or more conidia (Fig. 

 104, 1). The conidia, which fall off readily, are produced 

 until the latter part of summer, when the filaments which 

 bear them shrivel up and disappear. 



330. During the latter part of summer spore-sacs are 

 produced, but require the greater part of winter to come to 

 perfection. The spore-sacs grow in the cavities of minute 

 papillae (perithecia), and are intermingled with slender fila- 

 ments (paraphyses, 3 and 4, Fig. 104). Each spore-sac 

 contains eight spores, which eventually escape through a 

 pore in the top of the sac. These spores germinate by 

 sending out a small filament, or sometimes two (Fig. 104, 6). 



331. Besides the perithecia, there are other cavities 



