100 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in their course and transmission through different species of living 

 bodies, modified properties have been acquired either in a single 

 or several species, and whether by a selected reversal of the mode of 

 life a reversion to harmlessness can be induced in the virulent forms, 

 are questions of serious import that lie in the future. To those 

 interested in the question of germicides (sporocides) and antiseptics, 

 we may refer to an article by Dr. Miquel,* the able observer at the 

 Montsouris Observatory, Paris, who has largely extended the list, 

 which is headed by biniodide of mercury. 



Those who are in want of a subject for investigation may be 

 strongly advised to cultivate an acquaintance with the pages of this 

 valuable work, and add their own independent observations to the 

 list of original articles of which there is a very copious bibliography 

 brought down to a very late period. Dr. Sternberg can be congratu- 

 lated on giving us a well illustrated and most readable addition to 

 the literature of the bacteria with valuable information derived from 

 his own careful experiments. , 



Lichens s. 



Cephalodia of Lichens.! — K. B. J. Forssell proposes to confine the 

 term Cephalodia to those structures which contain one or more algae, 

 the type of which differs from the normal gonidia of lichens, and 

 which have been formed by the mutual action of hyphse and algae. 

 Cephalodia have been at present observed in one hundred species of 

 algae, but belonging to only a few genera. They appear to occur 

 chiefly in the Archilichenes. Those described in other families have 

 mostly not been properly cephalodia, where the hyphae always obtain 

 a stronger development from contact with the algae ; as Peltigera 

 canina, where the hyphae serve to nourish the algae, or Solorinella 

 asteriscus, where they are indifferent to one another. 



The position of the cephalodia varies ; they occur sometimes in 

 the under, sometimes in the upper side of the thallus, sometimes on 

 or in it ; occasionally also in the protothallus. They usually form 

 protuberances of a dark yellowish-red or dark red colour in the upper 

 side of the thallus. When the cells of the algae which form cepha- 

 lodia come into contact with the hyphae the hyphee develope rapidly, 

 involve the algal colony, and become copiously branched. The cells 

 of the algae divide at the same time, thus increasing the size of the 

 cephalodium by mutual symbiosis. Most cephalodia are formed by 

 the mutual action of algae and of hyphae which belong to an already 

 developed lichen-thallus (cephalodia vera). Among these the author 

 distinguishes between cephalodia epigena or perigena, formed on the 

 upper side of, or upon, the thallus, as in Peltidea aphtosa, Sphcero- 

 phorus stereocauloides, and Stereocaulon ramulosum ; and cephalodia 

 hypogena, formed on the under side of the thallus. There are 

 differences again among these. Sometimes {Solorina octospora) the 

 cephalodium lies at the base of the medullary layer ; sometimes 



* ' La Semaine Medicale,' 30 Aout, 1883. 



t Bihang till K. Svenska Vet. Akad. Handl., viii. (1883) 112 pp. (2 pis.). 

 Bee Bot. Centralbl., xv. (1883) p. 330. 



