i9H] CURRENT LITERATURE 373 



I 



is a partial alveolization and anastomosing of the chromosomes, but no com- 

 plete resting stage. The second or homeotypic division follows very quickly. 



Extranuclear nucleoli appear about the time of the second contraction, and 

 are seen at all subsequent stages with the exception of the metaphases of the 

 two mitoses. It is thus held to be not improbable that there is some connection 

 between the substance in these bodies and that of the spindle. 



The foregoing results are of interest in connection with the observations 

 which the reviewer 2 has made on the nearly related Vicia Faba. In this 

 species there is a very clear conjugation of leptonema threads before synizesis, 

 many more stages in the somatic prophase, and a much more definite size 

 difference in the chromosomes, both in somatic and in maturation mitoses, 

 than Sakamura has shown in Vicia Cracca. These facts have led the reviewer 

 to believe either that the latter species is not so favorable as an object for 

 study as Vicia Faba, or that there are to be made out many more details than 

 Sakamura has represented in his rather inadequate series of figures. — L. W. 



Sharp. 



Sporogenesis in Equisetum. — In the third of a series of studies in spore 

 development, Beers gives an account of sporogenesis in Equisetum arvense. 

 In the premeiotic cells the spirem, discontinuous from the first, arises from the 

 reticulum by condensation and the breaking down of anastomoses along certain 

 lines. The spirem segments appear to be unsplit until they become arranged 

 on the spindle in the form of definite chromosomes. At telophase the chromo- 

 somes develop a reticulum by the formation of numerous anastomoses, but 

 without internal vacuolation. 



In the spore mother cell the discontinuous spirem is formed from the reticu- 

 lum during synizesis. A longitudinal split visible during the early stages dis- 

 appears as the spirem thickens. In a former note, Beer held this to represent 

 parasynapsis, but as a result of the present study he has altered his opinion 

 with regard to the origin of the heterotypic chromosomes. He now takes the 

 view of Farmer, and believes they arise by the folding together of pairs of 

 somatic chromosomes placed end to end in the spirem, the folding occurring 

 at the time of the second contraction. During this period the nucleolus gives 

 off material which appears to contribute to the growth of the chromatic threads. 



The spindle is formed in the manner described by Osterhout, with no 

 centrosomes. The two maturation divisions occur as usual, but with an inter- 

 vening resting stage. After the second division the resting reticulum is devel- 

 oped in the same manner as in somatic cells. — L. W. Sharp. 



Sharp, L. W., Somatic chromosomes in Vicia. La Cellule 29:297-331. pis. 2. 



r 9i3- 



, Maturation in Vicia. (Prelim, note.) Bot. Gaz. 57:531. 1914- 



3 Beer, R., Studies in spore development. III. The premeiotic and meiotic 

 nuclear divisions of Equisetum arvense. Ann. Botany 27:643-661. pi . 51-53. i9 x 3- 



