242 BOTANICAL GAZETTE [SEPTEMBER 
The work from BLACKMAN’s laboratory has done much to substitute a 
physico-chemical conception for the too general stimulus conception of the 
German plant physiologists. In this direction these papers again bring forth 
evidence for the non-existence of true optima, for the great importance of 
“limiting factors,” and for the significance of what BLACKMAN has designated 
as the ‘‘time factor.”—WILLIAM CROCKER. 
Cytology of the ascus.—The controversy to which the behavior of the ascus 
nucleus has recently given rise, has led GUILLIERMOND* to reinvestigate the 
bject. Contrary to the results of Miss FRASER??: 23, 24 and her coworkers, 
these new observations extend and entirely confirm his previous studies, and 
convince him that the number of chromosomes remains constant during the 
three successive mitoses of the ascus nucleus. He discusses the method of 
formation and the separation of the chromosomes of the first division, and 
whether there exists a second: numerical reduction during the third nuclear 
division. In all of the species studied (Humaria rutilans, Peziza catinus, 
Pustularia vesiculosa, Galactinia succosa), he finds that the number of chro- 
mosomes of the equatorial plate stage and of the anaphases remains the same, 
and that the distribution of these chromosomes is accomplished in the same 
way in all of these forms. As in previous studies, GUILLIERMOND?S: 2° believes 
that the process described by Marre??: 28 that is, a double longitudinal division 
of the chromosomes during the anaphases, which results in doubling the num- 
ber of chromosomes found in the ee plate stage, rests on incorrect 
observations. He also believes that Marre’s contention that there exists in 
the ascus of Galactinia succosa protochromosomes, which fuse into four definite 
chromosomes, is untenable. GUILLIERMOND holds that there are eight definite 
chromosomes and not four, which are formed directly and not from proto- 
chromosomes. These eight chromosomes are divided only during the meta- 
2 GUILLIERMOND, M. A., Apercu sur l’évolution nucléaire des ascomycétes et 
nouvelles observations sur in mitoses des asques. Rev. Gén. Botanique 23:89-120. 
IgIo. 
22 FrASER, H. C. I., Contributions to the cytology of Humaria rutilans. Ann. 
Botany 22:35-55. 1908. 
73 FRASER, H. C. I., and WeEtsForp, E. J., Further contributions to the cytology 
of the ascomycetes. Ann. Botany 22:465-477. 1908. 
24 Fraser, H. C. I., and Brooxs, W. E. Sr. J., Further studies on the cytology 
of en ascus. Ann. Botany 23:538-549. 1909. : 
UILLIERMOND, M. A., aoe sur la karyokinése des ascomycétes. Rev. 
om Sepsis 16:1-65. 190. 
, Remarques sur i karykinése des ascomycétes. Ann. Mycol. 3:344- 
361. 1905. 
27 Marre, R., Recherches cytologiques sur quelques ascomycétes. Ann. Mycol. 
3: pe aae 1905. 
, Recherches sur la karyokinése chez les ascomycétes. Rev. Gén. Bota- 
nique pits esis. 1904. 
