OF ARTS AND SCIENCES. 15 



III. 



CONTRIBUTIONS FROM THE CRYPTOGAMIC LABORATORY OF 

 HARVARD UNIVERSITY. 



XL — ON THE CARPOLOGIC STRUCTURE AND 



DEVELOPMENT OF THE COLLEMACEiE 



AND ALLIED GROUPS. 



By W. C. Sturgis. 



Presented by W. G. Farlow, April 9, 1890. 



Of the many questions which, during the last half-century, have 

 aroused more than a passing interest among mycologists, none have 

 received more attention or excited more controversy than those relat- 

 ing to the nature and development of lichens. Such questions natu- 

 rally present themselves under two phases, — the anatomy of the 

 thallus, including the nature and mutual relationship of its component 

 parts, and the origin and development of the fructification. Inasmuch 

 as it is chiefly under the latter phase that the subject is presented in 

 the present paper, it will be necessary to trace but briefly the course 

 of the investigations which have led to the conclusion now generally 

 accepted with regard to the nature of the lichen-thallus. 



As is well known, the thallus of lichens is composed mainly of two 

 elements, — a mycelial weft of hyphae similar to ordinary fungus-hy- 

 phae, and roundish cells of a grass-green or bluish-green color, existing 

 either in a unicellular condition, or united into groups or into monili- 

 form series of various types. According to the views of Fries,* pub- 

 lished in 1831, and accepted as conclusive from that time until the 

 year 1869, these green cells, the so-called gonidia, "are on the one 

 hand nourishing organs of the thallus, and on the other hand non- 

 sexual reproductive organs, which develop into new individuals either 

 before, or subsequent to, their separation from the mother plant," It 

 is hardly necessary to state that this view expresses the explanation 

 at that time accepted of the origin and function of the gouidia of 

 lichens, and their aggregation into the so-called " soredia." 



Again as late as 1860 we find that this view of the nature of the 



* Fries, Lichenographia Europsea Reformata. 



