8o 



however, algal cell-proliferation is very much retarded in the fully 

 developed portions of the thallus. The arrangement of the algae 

 into distinctly marked layers is simply the morphological expression 

 of the assimilative function in its relation to the lichen-structure as a 

 whole. In general the analogy between typical foliage leaves and 

 lichen-thalli is so striking that the student will have no difficulty in 

 comprehending the relative functional activities of the various struc- 

 tures. 



V. THE SPERMAGONIA. 



The spermagonia are minute structures occurring upon the 

 thallus of many lichens and are usually more numerous near the 

 margin of the thallus. They resemble certain little known struct- 

 ures met with in fungi and are similar to the spermagonia of Aeci- 

 dium. They appear as minute black cups sunk into the upper sur- 

 face of the thallus, opening by an apical pore. The sterigmata upon 

 which the spermatia are borne are formed internally ; the latter 

 are slender acicular straight or curved spore-like bodies, which at 

 maturity escape from the pore. 



As has been stated, Stahl, and more recently Sturgis, looked 

 upon the spermatia as the male reproductive organs of the collema- 

 ceous lichens, but in spite of their trustworthy observations other in- 

 vestigations would seem to indicate that the spermagonia are neither 

 more nor less than parasitic fungi of which the spermatia are the 

 spores. DeBary has clearly shown that the spermagonia of certain 

 fungi are true parasites. It has also been repeatedly observed that 

 the spermatia will develop into a mycelial network. From a com- 

 parative study it seems probable that the spermagonia are fungi allied 

 to the genus Sejbtoria. For example, Sej)toria S^peculariae pre- 

 sents the general morphological characters of most spermagonia. 

 In the case of this fungus the morphological and physiological con- 

 trasts between host and parasite are great, while in the case of the 

 spermagonia these contrasts are only slight. It was impossible to 

 demonstrate that the hyphae of the spermagonia are organically con- 

 tinuous with the tissue of the lichen. 



For the sake of completeness, we will briefly explain Stahl's 

 conception of reproduction among certain lichens (Collema). The 

 first beginning of the apothecium takes its origin from medullary 

 hyphae near the middle of the thallus ; it consists of a colorless hy- 

 phal branch, rather thicker than the normal hyphae, which after form- 



