118 



SCIENCE. 



[N. S. Vol. XXIV. No. 604. 



pied by the railroad and between Nogales and 

 Imuris, one sees near the mountain bases low 

 benches which have been eroded into overlap- 

 ping oblique ridges of which the material 

 seems to be all of morainal character. These 

 overlapping ridges form prominent features 

 in the landscape and are locally called by the 

 Mexicans cordones, or 'chains.' They have 

 not been observed by the writer south of 

 Magdalena, 



In traveling eastward from Benson toward 

 El Paso, at a few points, mountain masses 

 were observed, rising from the desert plains, 

 around the bases of which were slightly ele- 

 vated benches corresponding in some measure 

 to the bench of morainal material along the 

 eastern base of the Santa Rita Mountains. 

 Occasionally, also, the railroad cut through 

 low rolling ridges of material, morainal in 

 structure and clearly not formed by sheet flood 

 erosion. 



On the Rock Island Railway, about a mile 

 southwest of Santa Rosa, N. M., near the 

 southeastern bank of the Pecos River, is a 

 train of rolling hills which show morainal 

 structure in the railroad cuts. 



These observations lead to the conclusion 

 that the quaternary history of some portion 

 of this region is more complex than has been 

 supposed. Clearly before the present period 

 of arid climate and periodic sheet flood ero- 

 sion was a time of low temperature and accu- 

 mulated precipitation in the form of land ice 

 which resulted in the formation of extensive 

 deposits of rock debris around the bases of at 

 least the higher mountain ranges. Climatic 

 conditions limited the extent of these moraines 

 so that the present desert basin areas, in many 

 cases, remained unglaciated. 



A further point of interest is the hypothesis, 

 . suggested by the facts observed, that some of 

 the quaternary conglomerates which are abun- 

 dant in northern Sonora and are so puzzling 

 in respect to their origin may in part be the 

 result of glaciation. The writer has, so far, 

 been unable to formulate any other theory of 

 origin which will account for the presence, in 

 some of these beds, of boulders as large as 

 two feet in diameter, in a matrix of angular 



fragments, of many different kinds, mingled 

 with fijie material. In a bed of true volcanic 

 breccia one does not ordinarily find several 

 different kinds of eruptive rock varying great- 

 ly in composition. 



Frederick J. H. Merrill. 

 New Yoek Citt. 



zygospores and sexual strains in the common 



bread mould, RHIZOPUS NIGRICANS.^ 



From the preliminary communication of J. 

 I. Hamaker in the May 4 number of Science, 

 entitled ' A Culture Medium for the Zygo- 

 spores of Mucor stolonifer ' (Bhizopus nigri- 

 cans), one would be led to suppose that the 

 method of obtaining the zygospores of this 

 species by admixture of strains from different 

 sources was unnecessarily troublesome and un- 

 certain. After having obtained the zygo- 

 spores frequently for three months, he is 

 brought to the. conclusion, which is printed in 

 italics, that 'with proper conditions of mois- 

 ture and temperature, success is apparently 

 dependent only on the nature of the sub- 

 stratum.' As a favorable substratum, a corn 

 muffin bread is recommended and a detailed 

 formula of the ingredients is given. 



In a preliminary summary of a study of the 

 sexual conditions in the Mucorinese,'' the 

 present writer has used this same common 

 bread mould Bhizopus nigricans, as a type of 

 the heterothallic {i. e., dioecious) group in 

 which each species is to be considered an 

 aggregate of two distinct sexual strains the 

 interaction of which is requisite to zygospore 

 formation. In contrast to homothallic (i. e., 

 hermaphroditic) species in which the mycelia 

 are sexually all equivalent and which may 

 produce zygospores from the sowing of a single 

 sporangiospore, it is necessary in the hetero- 

 thallic species, in order to obtain the zygo^ 

 spores in pure cultures, to sow spores together 

 from both the sexually opposite strains which 

 have been provisionally designated by the terms 



^ This paper was written while working under 

 a grant as research assistant to the Carnegie In- 

 stitution. 



* ' Zygospore Formation a Sexual Process,' Sci- 

 ence, N. S., 19: 864-866. 1904. 



