RECENT RESEARCHES INTO THE NATURE OF LICHENS. 153 



points out that there are several difficulties in the natural history 

 of Lichens with which the Schwendenerians have to deal^ as, for 

 instance, the case of Athalline Lichens that have neither hyphse 

 nor gonidia, that are represented, in fact, only by apothecia — 

 and for examples he refers to Archer's paper which has been con- 

 sidered above. It must be remarked that the author appears 

 to have overlooked the conclusions at which Archer arrived. 

 He finishes his letter by comparing Schweudener with Bayrhoffer ! 



An interesting paper was contributed later on in the year by 

 Prank. ^ As the result of his observations on the development 

 of the gonidia he states that there two ways in which they are 

 formed in the lichen-thallus ; (1) usually they are derived from 

 those already existing in the thallus; (3) they make their way 

 into the growing thallus from without, and then multiply. 

 Another mode of origin of gonidia was described about the same 

 time by Minks.^ According to his observations the germinating 

 spore gives rise to a mass of hyaline hyphse from which, together 

 with the coloured secondary hypha (which is probably connected 

 with the development of the apothecia) certain organs are formed, 

 — termed by him Gonangia and Gonocystia— within which 

 gonidia are formed by free-cell formation. 



In passing to the consideration of the papers published in 1877 

 upon this subject it is interesting to recall a sentence which 

 occurs in Lauder Lindsay's letter, already quoted. He says : " If, 

 by artificial cultivation, such a union {i.e., of Fungus and Alga) 

 could be made to produce a Lichen, the theory might he held as 

 proven." Such evidence is aft'orded by Stahl's^ paper on the 

 nature of hymenial gonidia, as the following account will 

 show. 



The experiments which had previously been made in this direc- 

 tion by Eeess, Bornet and Treub, had met with only partial 

 success. In all cases the lichen-spores after being sown upon 

 various Algse germinated, and their hyphse formed with the Algae, 

 a structure resembling in some degree the thallus of a Lichen, 

 but in no case was any fructification ever developed. Stahl's 

 researches upon the hymenial gonidia enabled him to overcome 

 the difficulties which had marred the success of the experiments 

 of his predecessors, and enabled him to trace the whole course 



* ' Ueb. d. biolog. Verhaltnisse des Thallus einiger Kriistenfleehten, 

 Colin's Beitrage,' Bd. ii. 



^ ' Beit. z. Kenut. des Baues und Lebens der Flechten, 1, Gonangium 

 und Gonocystium,' Wien, 1876. 



' • Beitrage zur Entiwickelungs-geschichte der Flechten, 1877.' 1. " Ueber 

 die geschlechtliche fortpflanzung der Collemaceen." 2. "Ueber die Bedeu- 

 tuug der Hymenial-goiiidien." The first of these papers will be dis- 

 cussed at another time. 



