330 



PRACTICAL COURSE IN BOTANY 



curled, giving them a somewhat leaflike appearance, whence 

 they are called " foliaceous " lichens. This broad, expanded 

 body is the thallus, or vegetative part, as distinguished from 

 its reproductive part. Examine carefully the thallus of 

 your specimen. Note the size and shape of the indentations. 

 Is there any order or regularity about them, such as was 

 observed in the lobing of leaves? Is there any difference 

 in color between the upper and under sides? What other 

 differences do you notice? Do you see anything like hairs, 

 or rootlets, on the under side ? Mount one of them in water 

 and place under the microscope. WTiat does it look like? 

 Compare with one of the hairs from a leaf of mullein, grom- 

 well, blueweed, or other hairy plant, with the hypha of a 

 fungus mycelium, and with your study of the root hair in 

 67 (a). Is it a hair or a root? These rootlike hairs are 

 called rhizoids, and serve to anchor the lichen to its substra- 

 tum. Look on the upper side for little cup-shaped or 

 saucer-shaped receptacles. On what part of the thallus 



are they situated? Ex- 

 amine with a lens and see 

 if you can make out what 

 they contain. These cups 

 are the spore cases. The 

 lichen fungus belongs to 

 the division of sac fungi, 

 which produce their 

 spores in closed sacs, or 

 cups. 



380. Structure of the 

 thallus. — Make a thin 

 section through a thallus and place under the microscope. 

 Notice the small green bodies enveloped in the hypha? of the 

 fungus. Are they most abundant near the upper or the lower 

 epidermis? Has their green color anything to do with this, 

 and with the difference in color between the two surfaces of 

 the thallus ? (184.) Do they look like chlorophyll granules ? 



Fig. 470. — Portion of the thallus of a lichen, 

 magnified, showing imprisoned algai. 



