732 THE AMERICAN NATURALIST. [VOL. XXXVIII. 



mass besides the nucleolus. The significance of synapsis is not 

 clear, but the subject will be discussed in Section VI. How- 

 ever, there is good evidence from Anthoceros that the phenome- 

 non is a normal event and not an artefact, because synapsis is 

 always found at a certain period of sporogenesis, and nuclei in 

 neighboring spore mother-cells a little older or younger present 

 their chromatic material with the usual arrangement (Davis, '99, 

 p. 96 and 97). 



To summarize the conditions in the spore mother-cells of the 

 Hepaticae, all conclusions, in the author's opinion, indicate : (i) 

 That the spindles develop from a surrounding weft of fibrillae 

 without the assistance of centrosomes. (2) That the mitoses 

 are always two in number and successive with the same number 

 of chromosomes for each division. (3) That the cell walls may 

 be formed successively as in Pellia and some other of the Jun- 

 germanniales or simultaneously, to give tetrahedral spores, as in 

 Anthoceros, types of the Marchantiales and Ricciales, Pallavi- 

 cinia and some companion forms in the Jungermanniales. It 

 will be interesting to note the essential agreement in these 

 matters between the Hepaticse and the higher plants. 



Nothing is known of the nuclear activities during sporogenesis 

 in the other great division of the bryophytes, the mosses 

 (Musci). The spore mother-cells in this group are always small 

 and unattractive for cell studies but the Sphagnales appear to be 

 rather the most promising for such investigations, which are 

 greatly to be desired. 



The pteridophytes have furnished some important contribu- 

 tions to our knowledge of the spore mother-cell. There is first 

 the paper of Osterhout ('97) on spindle formation in Equisetum, 

 which was one of a group of three contributions (Mottier, '97, 

 Juel, '97) that did much to dispose of a then prevalent belief 

 that the development of the spindle in higher plants was con- 

 trolled by centrosomes. This investigation was followed by 

 a study of Smith (: oo) on spindle formation in Osmunda. 

 Calkins ('97) and W. C. Stevens ('98^) considered especially 

 the formation and reduction of chromosomes in several of the 

 ferns, and arrived at contradictory conclusions. Strasburger 

 (: oo, p. 76 to 79) has reviewed these results in relation to 

 studies of his own on Osmunda. 



