122 MOSSES AND FERNS chap. 



flattened. The nucleus of the cell lies in close contact with the 

 chloroplast, and usually partly or completely surrounded by it. 

 There is no separation of the tissues into assimilative and 

 chlorophylless, as in the Marchantiaceae, and in this respect 

 Anthoceros approaches the simplest Jungermanniaceae, as it does 

 in the complete absence of ventral scales or appendages of any 

 kind, except the rhizoids. 



The infection of the plant with the Nostoc has been carefully 

 studied by Janczewski ^ and Leitgeb.^ The infection takes 

 place while the plant is young, and is usually brought about by 

 a free active filament of Nostoc making its way into the 

 intercellular space below the mucilage slit, through whose 

 opening it creeps. Once established, the filament quickly 

 multiplies until it forms a globular colony. The presence of 

 the parasite causes an increased growth in the cells about the 

 cavity in which it lies, and these cells grow out into tubular 

 filaments which ramify through the mass of filaments, and be- 

 come so interwoven and grown together that sections through 

 the mass present the appearance of a loose parenchyma, 

 with the Nostoc filaments occupying the interstices. Other 

 organisms, especially diatoms and OscillarecB, often make their 

 way into the slime cavities, but according to Leitgeb's investi- 

 gations their presence has no effect upon the growth of the 

 thallus. 



The plants are monoecious in A. fusiformis, and this is 

 true of other species observed. In the former, however, the 

 antheridia appear a good deal earlier than the archegonia. I 

 observed them first on young plants grown from the spores, 

 that were not more than 3 mm. in length. The exact origin 

 of the cell from which the antheridia develop could not be 

 made out, as none of my sections showed the youngest stages. 

 Waldner's ^ observations upon A. l(Bvis, however, and my 

 own on NototJiylas valvata, as well as a study of the older 

 stages in A. fusiformis, leave no doubt that in this species as 

 in the others the antheridia are endogenous, and the whole 

 group of them can be traced back to a single cell. They arise 

 close to the growing point, and the cell from which they arise 

 is the inner of two cells formed by a transverse wall in a 

 surface cell. The outer cell (see figure of Notothylas') divides 



^ Janczewski (i). - Leitgeb (7), vol. v. p. 15. 



3 Waldner (2) ; see also Leitgeb {7), vol. v. p. 15. 



