28 GUIDE TO THE STUDY OF LICHENS. 



convert the independent chlorophyll-bearing organism 

 into a dependent chlorophylless organism. 



The above is in brief the history of the origin and 

 development of all vegetable parasites. Even now we 

 can find all gradations between parasitic states just 

 making a beginning, as, for example, some species of 

 Nostoc and Protococcus, and the most highly developed 

 parasitism, as, for example, most of the fungi. Sapro- 

 phytes differ from parasites only in that the originally 

 green, hence chlorophyll-bearmg plants, became adapted 

 to live upon dead organic matter rather than living 

 organisms. It must also be kept in mind, that as par- 

 asitism and saprophytism progressed the resulting 

 fungi underwent structural changes ; so that it is in 

 many instances practically impossible to recognize the 

 resemblance to any living forms of algae. Scientists 

 are, however, quite generally agreed that fungi are 

 derived from algae. 



As a rule, fungi reproduce their kind by means of 

 very minute microscopic bodies known as spores. All 

 of the higher fungi may be divided into two groups 

 according to the manner in which the spores are formed ; 

 in the one group they are formed on the ends of spe- 

 cialized hyphae, known as hasidia, in the other group 

 they are formed within specialized hyphee, known as 

 spore-sacs (Asci). The latter are therefore commonly 

 known as sao-fungi. We have to deal with the sac- 

 fungi (Ascomyctes) only. There is, however, one 

 Southern lichen ( Cord) which forms basidio-spores. It 

 is the only exception occurring in the United States 

 and is, furthermore, of rare occurrence. Keeping, there- 



