(H4) 



plants known as bacteria. This peculiar growth is com- 

 monly known as vegetable cancer on account of its close 

 resemblance to the cancer of the human body. The 

 disease is very destructive to trees and shrubs of various 

 kinds. Second we have the stalked-spored fungi (cases 16 

 to 29). This series falls into two groups, the one typified 

 by the "rusts" and "smuts" which are commonly para- 

 sitic on the leaves and fruits of other plants; the other the 

 great saprophytic group, well known through the mush- 

 rooms, bracket-fungi, stink-horns, and puff-balls. Third in 

 this series are the spore-sac fungi (cases 30 to 35). In these 

 plants the spores are borne in delicate membranous sacs, 

 called asci, which in the more complex forms are collected 

 into bodies of various shapes. The plants vary greatly in 

 size and structure and may be either parasitic or saprophytic. 

 To this group belong the yeasts and mildews; and also the 

 chestnut-blight fungus. This disease, which has been im- 

 ported into this country, has caused the death of all of the 

 American chestnut trees in the immediate vicinity of New 

 York City and threatens the entire destruction of this valu- 

 able tree. Some plants grow above the surface of the ground, 

 as in the case of the morel; while others are subterranean, 

 as in the case of truffles. Fourth in the series is the group 

 known as the imperfect fungi (case 36). In this group the 

 spores are borne directly on the threads or "hyphae" 

 which constitute the vegetative portion of the organism. 

 They are often parasitic on the leaves and on the bark 

 of both wild and cultivated plants. The fifth and in many 

 respects the most interesting of all the groups is that con- 

 sisting of the lichens (cases 37 to 40). The lichens have 

 commonly been considered to form an independent sym- 

 biotic group, each lichen being supposed to consist of a 

 fungus and an alga living together, the one nourishing the 

 other, but, according to some of the more recent students 

 of the group, the lichens are simply fungi that live parasiti- 

 cally upon algae. The lichens are quite familiar to most 

 people as plants of more or less leathery texture growing on 

 rocks, on poor soil, or on the trunks of trees. 



