220 PHYLUM VII. CARPOMYCETEAE 



ally penetrate downward some centimeters 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. 



359. To this order belongs the Ergot (Claviceps), a 

 common parasite 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. 



360. The Closed Fungi include a large number of 

 exceedingly injurious species; they often attack and 

 destroy not only plants, but also insects, upon which 

 their ravages are sometimes very great. 



THE MILDEWS (ORDER PERISPORIALES) 



361. These plants, which are mainly parasitic, are 

 composed of branching septate filaments (hyphae) which 

 form a white or dark web-like film upon the surface of the 

 leaves and stems of their hosts. There are both sexual 

 and asexual spores, and of the latter there are in some 

 cases two or three different kinds, which are produced 

 earlier than those that result from a fertilization. 



362. In the Powdery Mildews (Family Erysiphaceae) , 

 which are all parasitic, the jointed filaments closely 



cover the leaves and other tender parts 

 of many plants, and draw nourishment 

 from them by means of suckers (hausto- 

 ria), which project as irregular out- 

 growths from the side next to the epi- 

 dermis. These suckers apply them- 

 selves closely to the epidermal cells, and 

 penetrate them. 



363. The crossing and branching filaments soon send 

 up many vertical branches, which continue to form new 



