128 MOSSES AND FERNS CHAP. 



Each cell of the thallus contains a single chloroplast which 

 may be either globular or spindle-shaped, or more or less 

 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 Marchantiacese, 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 care- 

 fully studied by Janczewski and Leitgeb ( (7), v., p. 15). 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 becomes so interwoven and grown together that sections 

 through the mass present the appearance of a loose par- 

 enchyma, with the Nostoc filaments occupying the interstices. 

 Other organisms, especially diatoms and Oscillarccc, often 

 make their way into the slime cavities, but according to Leit- 

 geb's investigations their presence has no effect upon the 

 growth of the thallus. 



Sexual Organs. 



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 which the antheridia develops could not be made 

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

 Waldner's (2) observations upon A. Iccvis, however, and my 

 own on A. Pearsoni and Notothylas 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 



