CARPOPHYTA. 165 
Possibly they exist in the dense tissues of the knot, and 
fertilization probably occurs in the spring or early summer, 
while the conidia are being produced on the surface of the 
young knot. 
345. The parasitic filaments of each year’s knot gener- 
ally penetrate downward some centimetres into the unin- 
jured bark, and remain dormant there until the following 
spring, when they begin the growth which results in the 
production of a new knot, as described above. 
346. The Black Fungi include a large number of exceed- 
ingly injurious species; they often attack and destroy not 
only plants, but also insects, upon which their ravages are 
in many cases very great. 
347. To this order belongs the Ergot (a2 common para- 
site upon heads of rye), and also many of the black growths 
upon the bark and wood of trees. Many species produce 
black spots upon living leaves, while many others occur 
upon dead leaves and twigs. 
Practical Studies.—(a) In early summer examine the Choke-cherry 
and Plum trees (wild and cultivated) for the young stages of Black 
Knot. Watch the development until the knot becomes velvety in ap- 
pearance (about midsummer). Now make very thin cross-sections 
of the knot and examine for conidia. 
(0) Late in autumn and in early winter examine the knots on the 
same trees. Note the young perithecia, i.e. hollow papille. Make 
very thin vertical sections through some of these. No perfect spores 
can be found at this time. 
(c) Collect fresh knots in midwinter and make similar examina. 
tions, when the sacs and spores will be found. 
Notre.—The several stages may be readily preserved in alcohol for future 
study. 
348, The Lichens (Order Lichenes) are among the most 
interesting plants of the vegetable kingdom. They are not 
only often of exceeding beauty, but their structure and 
their mode of life are in some respects very wonderful. 
