32 PROCEEDINGS OF THE AMERICAN ACADEMY 



and development of the apothecium seem to be purely vegetative pro- 

 cesses, nor, as fur as I have observed, is there any distinction, at any 

 stage in the development, between the ascogenous and the enveloping 

 systems of hyphae. Owing to the gelatinous quality of the membranes 

 of the paraphyses, and the frequent fusion of their tips, it is a matter 

 of much difficulty to separate the elements of the hymenium and trace 

 them to their origin. This may be done, however, as in Nephroma, 

 by careful crushing, after treatment with potassic hydrate and tlien 

 with an aqueous solution of iodine and potassic iodide. The blue 

 coloration of the asci is as permanent as with the tincture of iodine. 

 The coloration of the protoplasm, however, is readily washed out by 

 the subsequent treatment with water, though this will be found to be 

 no particular disadvantage. (Plate I. Figs. 7, 8.) 



Thus far we have considered types of genera which present on the 

 whole the structural characteristics of the heteromeric, foliaceous 

 lichens. But we have already seen tendencies toward another type. 

 In Nephroma tomentosum we have seen that the algJB forming the host 

 are no longer of the grass-green, unicellular type, but are bluish-green 

 cells united into colonies, and belonging evidently to the phycochro- 

 maceous genus Gloeocapsa, Nag., and the same is true of many species 

 of the genus Peltigera. In fact, the family to which this latter genus 

 belongs presents in a very marked degree this transitional character 

 with respect to the gonidia. Three of the five genera included in it 

 by Tuckerman are characterized by bluish-iireen algfe in one group of 

 species and grass-green algfe in another group ; another genus possesses 

 both types of algte in one and the same species, while the fifth genus 

 is parasitic on bluish-green alga3 alone. Coming to the family Panna- 

 riei, however, we find this transitional feature even more strongly 

 marked, one only of the four genera being in part parasitic on grass- 

 green algae. Furthermore, we shall see that in this genus we begin to 

 lose sight of the Chroococcus and Gloeocapsa types of algae, and find a 

 marked approach toward the homa>omeric lichens in the occurrence 

 of a filamentous type of alga. Finally, in the loss of the lower cor- 

 tex in the genus Peltigera, we must recognize an added link in the 

 chain of evidence connecting the heteromeric with the homoeo- 

 meric lichens. 



