MOULDS, KUSTS, ETC. 115 



by no means certain that we are yet in possession of all of the facts. 

 The habits of the group to which it belongs present an attractive and 

 difiBtOTllt field for special research. 



LICHENS. 



Scrape off some of the grayish-green or yellowish lichens 

 that form incrustations on old fences and the bark of trees ; 

 take a small fragment and tease with needles until it is thor- 

 oughly separated, and then examine with the compound 

 microscope. It will be found that the lichen thallus, what- 

 ever species has been selected, is composed of two distinct 

 elements, first a fungus, the hyphse of which form a con- 

 fused and compact felt ; and second, numerous rounded, 

 green cells which have all the characteristics of algae. 

 Notice carefully the mode of connection of fungus and 

 alga. Find a place where the elements are isolated as 

 much as possible, and draw. 



Repeat the study, using other species, and then describe 

 from your own observation the habits, external features, 

 such as form, color, and texture, and the anatomical struc- 

 ture of a lichen thallus. 



Note. — A complete study of the fructification of lichens requires 

 more time than is likely to be available in an elementary course. Accord- 

 ingly further directions are omitted, but teachers who choose will of 

 course proceed with their classes to the examination of the apothecium 

 and to such further studies as they deem most profitable. Strasburger's 

 Praktikum and other manuals give further suggestions. 



REVIE"W AND SUMMARY. 



The black mould and the rust of wheat are common 

 representatives of an enormous group of plants, the fungi, 

 which are characterized, first of all, by absence character and 

 of chlorophyll, and consequent inability to manu- l^atits. 

 facture food in the same manner as green plants. Their 

 habits of life correspond with this limitation of function. 



