ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 829 



appears that the majority of the prothalli found owed their origin to 

 this source, and not directly to the germination of spores, a similar 

 phenomenon to that which occurs in the case of Gymnogramme 

 leptopliylla. The prothallus is as a rule devoid of chlorophyll, and 

 consists of cylindrical branches covered with absorbing hairs. These 

 cylindrical organs branch monopodially, the branches being usually 

 formed in acropetal order ; they have a terminal growth with two 

 initial cells, each of which gives rise to half of the cylindrical organ. 

 There is a great similarity between the structure of this apical 

 meristem and that of the stem of the sporophore. In the fully 

 differentiated parts of the prothallus a peripheral tissue one layer of 

 cells in thickness may be distinguished ; this gives rise to the 

 rhizoids. The mass of tissue inclosed by this superficial layer, 

 though it shows some slight varieties according to the mode of 

 development of the branch, never attains any high state of differ- 

 entiation. 



The lateral branches, which are not very numerous, take their 

 origin from the peripheral layer, several cells taking part in the 

 formation of each. The growth of these branches may be long-con- 

 tinued, and it is not arrested on the formation of an embryo on 

 another branch. By progressive rotting of the older parts, branches 

 may be separated from one another, and this constitutes the simplest 

 mode of increase in the number of individuals. But, besides this, two 

 other modes of vegetative propagation are known — (a) by ordinary 

 propagating organs : these are small ovoid multicellular bodies, 

 which originate from single superficial cells, and are set free by 

 rupture of their pedicels ; (&) by thick-walled organs, smaller than 

 the above, which only appear on weakly prothalli : these may undergo 

 a period of rest. Dr. Treub compares these structures to the gemime 

 of the Hepaticpe, and especially of Blasia ; while in many of their 

 general characters the prothalli of L. Phlegmaria show points in 

 common with the oophore of certain of the Muscinese. 



The sexual organs of L. Phlegmaria are produced on the upper 

 surface of the prothallus, and are always accompanied by paraphyses, 

 structures which are absent from other Vascular Cryptogams. The 

 position of the antheridia is variable ; sometimes they are scattered 

 singly on the vegetative branches, sometimes they are associated in 

 groups, and are then often borne on the considerably thickened ex- 

 tremities of branches. Their development is similar to those of 

 L. cernuum, while the antherozoids have two cilia, and resemble those 

 of Selaginella. The archegonia have a more definite position, and 

 they appear subsequently to the antheridia, on those thickened 

 extremities of branches which have already borne antheridia : they 

 project from the surface of the prothallus, and have three to five 

 canal-cells. This is again a point in common with certain Muscinea3. 



There is a considerable difference between the development of 

 the embryo in L. cernuum and that of L. Phlegmaria, while in certain 

 points the latter corresponds to Selaginella Martensii. Thus the 

 ovum in L. Phlegmaria divides first by a wall perpendicular to the 

 axis of the archegonium into two ; of these, the cell next the neck 



