IV THE JUNGERMANNIACE^ 93 



overlap the base of the seta. As in Targionia, and this is true 

 for the other Jungermanniaceae, the spore mother cells become 

 deeply four-lobed before the division of the nucleus takes place. 

 Farmer ^ has recently studied this carefully in Pallavicinia 

 decipiens and also in species of Amur a. In the former, previous 

 to the division of the nucleus, there is formed a " quadri-polar 

 nuclear spindle," which extends into each of the four divisions 

 or lobes of the cell. Then follows a division of the chromosomes 

 into four groups, apparently without the daughter nuclei first 

 assuming the resting stage, and these four groups of chromo- 

 somes travel to the four poles of the spindle and gradually as- 

 sume the form of resting nuclei, after which the division walls 

 are formed, completely dividing the cavity of the cell. The 

 division of the nucleus occurs very late here, sometimes the 

 thickenings upon the outside of the spores being indicated 

 before the primary nucleus divides. In Aneura Diidtifida^ the 

 formation of the quadri-polar spindle occurs, but there is after- 

 ward a formation of two distinct nuclear figures of the ordinary 

 type. 



The growth of the seta after the spores are ripe is ex- 

 tremely rapid, but consists entirely in a simple elongation of the 

 cells. Askenasi - has investigated this in Pellia epipliylla, and 

 states that in three to four days the seta increases in length from 

 about I mm. to in some cases as much as 80 mm., and that this 

 extraordinary extension is at the expense of the starch which 

 the outer cells of the young seta contain in great abundance, 

 but which disappears completely during the elongation of the 

 seta. The growing sporogonium here as well as in other 

 species is strongly heliotropic. 



The calyptra in the thallose Anacrogynae is usually massive, 

 and in addition there is formed about the growing sporogonium 

 a special envelope inside the involucre, which in Pallavicmia 

 especially (Fig. 38, A) becomes prolonged into a tube which 

 completely encloses the sporogonium until just before its 

 dehiscence. 



The further development of the spores and elaters corre- 

 sponds with that of the Marchantiaceae (Fig. '^j), and here there 

 is the same method of the development of the thickenings 

 upon the walls of the elaters and the spores. In cases where 

 the spores germinate immediately, chlorophyll is developed and 

 ^ Farmer (4). " Askenasi (i). 



