266 



SCIENCE 



[N. S. Vol. XXV. No. 633 



early days of the Christian era. The prac- 

 tise of all. early botanists was to regard all 

 forms in cultivation as distinct species. 

 Between thirty and forty specific names 

 have been applied to the plant and more 

 than one hundred trinomials in recent 

 years. Identity of the important species 

 and the natural method of classifying and 

 naming forms of a cultivated species. Use 

 of sorghum for human food, forage, syrup, 

 sugar, liquor, building material, firewood, 

 etc. 



Periodicity of the Sexual Cells of Dictyota 



dichotoma: W. D. Hoyt, Johns Hopkins 



University. 



On the coasts of "Wales and England 

 Dictyota dichotoma, according to Mr. J. 

 Lloyd Williams, bears its sexual cells in 

 regular fortnightly crops. The times at 

 which these crops are produced bear a defi- 

 nite relation to the tides, and the observed 

 behavior is best explained by regarding the 

 increased illumination obtained during the 

 low water of spring tides as the factor 

 which determines the time of fruiting. 



Observations made at the laboratory of 

 the Bureau of Fisheries, at Beaufort, N. C, 

 during the past summer show that at this 

 place also Dictyota dichotoma produces its 

 sexual cells in regular crops at periods 

 bearing a definite relation to the tides. 

 These crops, however, are borne at monthly, 

 instead of fortnightly, intervals, the time 

 of their production is not influenced by dif- 

 ferences in the height of different spring 

 tides, and it seems that light is not the 

 factor that determines the time of fruiting. 



Evidences of Sexual Reproduction in the 

 Slime-molds: Edgar W. Olive, Univer- 

 sity of MHsconsin. (Read by C. A. 

 King.) 



Some recent work on the exosporous 

 myxomyeete, Ceratiomyxa, has shown that 

 a simple form of sexuality exists in this 



form. Toward the close of the more or 

 less quiescent cleavage stage, the nuclei of 

 the Plasmodium fuse in pairs, so that the 

 uninucleate protospores which result from 

 cleavage each contain a large fusion nu- 

 cleus. The chromatin of this large nucleus 

 soon appears to become shrunken, or 

 rounded up in a dense ball, at one side of 

 the large nuclear cavity, thus resembling 

 strikingly the condition which has been 

 termed synaipsis. That this condition is 

 really a true synapsis, and not an artifact,- 

 is suggested by the two rapidly recurring 

 nuclear divisions which, after a short 

 period of rest, follow. These facts appear 

 to indicate that a reduction phenomenon 

 takes place at this time, similar to that 

 which takes place in the spore mother-cells 

 of higher plants. As a result of the double 

 division, each mature spore of the final 

 fructification comes to contain four nuclei. 



We thus note that in the life history of 

 this form, .we have presented the three mor- 

 phological stages, which, as pointed out 

 by Blackman and others, occur in connec- 

 tion with the complete sexual cycle, viz., 

 (1) cell fusions (when the many myxa- 

 moebse unite to form the Plasmodium) ; (2) 

 nuclear fusions (in pairs, near the close of 

 the development of the fructification) ; 

 followed immediately by the third stage, 

 chromatin fusion (associated with synapsis 

 and -the subsequent reduction division). 

 As has been pointed out, more or less wide 

 gaps may separate these successive stages 

 in- different plants. In Ceratiomyxa, we 

 obviously have a condition comparable to 

 that in the rusts, since cell fusion is far 

 separated from the final nuclear and 

 chromatin fusions. 



As Blackman has further pointed out, 

 the late nuclear fusion in the rusts has to 

 do with the reduction phenonema which 

 immediately follow, and he holds the opin- 

 ion that the stimulus to development — 

 fertilization proper — is imparted by the 



