6i8 THE POPULAR SCIENCE MONTHLY. 



ering is formed. This spore-case is shown more advanced in V. 

 Within, one or more sacs containing spores are formed. At II is seen 

 a mature spore-case which has been ruptured and a sac containing five 

 spores has nearly escaped. It is seen at a glance that the provision 

 made by these species of fungi for the protection of its spores during 

 winter is most complete. Each spore is, doubtless, surcharged with 

 vitality ; around it is a sac, and outside of this a thick, hard covering 

 not easily broken. Many of these spore-cases are provided with 

 hooked appendages, by means of which they may hold fast to rough 

 surfaces, and thus the contents are further protected. 



The black-knot {Sphceria morbosa), so injurious to the plum and 

 cherry trees, furnishes an illustration of another family of fungi, many 

 members of which are considered as pei-ennial. The fungus attacks 

 the young branches, causing them to swell to several times their natu- 

 ral size. The enlarged portion of the branch is made up of a vast 

 number of minute threads, which increase in length and size until 

 the bark of the twig is ruptured in one or more places. An olive-green 

 covering soon forms over the exposed part, consisting of spores borne 

 singly upon the tips of fungus-threads. These simple reproductive 

 bodies quickly pass away and spread the disease to other parts. Later 

 in the season the knot becomes incrusted and a second form of spore 

 is produced, very different in form from the simple oval ones already 

 mentioned. As autumn approaches, the knot assumes a black and 

 rough appearance, indicated in Fig. 10. In the hard crust small pits are 

 formed, in which spores are slowly produced within long, slender sacs. 

 These spores are not ripe until toward spring. In this well-named 

 black-knot we have a fungus with at least three forms of spores, one 

 of which serves the important purpose of carrying the species through 

 the winter season, in a form admitting of a ready dispersion in the 

 early spring. The knots last for more than one season, thus showing 

 that the whole community of fungus-life on a single plum or cherry 

 branch is perennial. This is well shown when a gardener fails to cut 

 away the branch for a sufficient distance below the affected part, in 

 which case the remaining end will develop into a well-formed knot 

 the following season. The filaments of the fungus extend for a foot 

 or more below the swelling, and live on from year to year. 



Belonging to the same great group of fungi with the black-knot, but 

 furnishing a different illustration of our subject, is ergot ( Claviceps 

 X>iirpurea). This fungus attacks the young female portion of the 

 flower of many grasses, and replaces the grain with a hard, irregular 

 mass, several times the size of the iinaffected grain. From the resem- 

 blance of these grains to the spurs of a cock, and because they are 

 most abundant upon the rye, the fungus has received the common 

 name of "spurred rye." Fig. 11 shows a head of rye, natural size, 

 with four of its grains ergoted. Multitudes of minute spores are pro- 

 duced upon the surface of the affected grain during the growing sea- 



