Pebbuaby 22, 1907] 



SCIENCE 



285 



The granules then fuse together to form 

 a firm, deeply staining, homogeneous ring 

 which is the blepharoplast, and lies very 

 close to the plasma membrane but is not a 

 part of it. The fibrils which connect the 

 blepharoplast with the nucleus disappear 

 and the nucleus somewhat later passes back 

 to the center of the spore. The blepharo- 

 plast now splits into two rings, one di- 

 rectly below the other. Cilia grow out 

 from the lower ring forming a circle 

 around the zoospore, which is about one 

 half the diameter of the latter. 



Sexuality in the Mucors: Dr. A. F. 



Blakeslee, Harvard University. 



The Mucors are divided into two groups 

 termed respectively homothallic and hetero- 

 thallie. In the homothallic group, zygo- 

 spores are developed from the same thallus 

 and can be obtained from the sowing of a 

 single spore. In the heterothallic group, 

 which comprises a large majority of the 

 species, zygospores are developed from 

 branches which necessarily belong to thalli 

 diverse in character and can never be ob- 

 tained from the sowing of a single spore. 

 Every heterothallic species is therefore an 

 aggregate of two distinct sexual strains 

 through the interaction of which zygospore 

 production is brought about. 



In the heterothallic species Mucor Mu- 

 cedo; the segregation of sex is completed at 

 or before the germination of the zygospore 

 and all the spores in a given germ sporan- 

 gium are of the same strain, either male or 

 female. 



In the germination of the zygospores of 

 the heterothallic species Phycomyces, a 

 segregation of sex takes place at the forma- 

 tion of spores in the germ sporangium 

 which contains both male and female 

 spores. The liverwort Marchantia poly- 

 morpha has been found to correspond to 

 this latter type of zygote germination and 



male and female spores are contained in a 

 single capsule. 



Cultures were exhibited showing dark 

 lines of zygospores between male and 

 female strains of the same species and 

 white lines of imperfect hybrids between 

 male and female strains of different species. 

 Microscopic preparations of zygospores of 

 various species were also exhibited. 



The Teaching of the Subject of Respira- 

 tion: Professor Charles H. Shaw, 

 Ursinus College. 



The word respiration is used in several 

 different senses. A confusion of ideas also 

 exists. Except in connection with highly 

 differentiated animals, the term respiration 

 must signify either a gaseous interchange, 

 or a metabolic process of energy release. 

 The former definition lends itself to clear 

 statement, is readily developed from exper- 

 iments, and refers to a process which is 

 really a non vital one. The latter, though 

 not so easy to teach, refers to the essential 

 process. For several reasons it is thought 

 that the latter will stand. At all events the 

 process of energy release must occupy the 

 central place in teaching. 



It is sometimes said that in respiration 

 CO2/O2 = 1, and also that all protoplasm 

 must obtain oxygen somehow all the time. 

 Such formal ideas will not square either 

 with the published facts upon the subject 

 nor with class-room experiments. 



The subject is worthy of a more ade- 

 quate treatment in general courses. Eu- 

 diometers over mercury with the seeds held 

 up by glass wool are one favorable form of 

 apparatus for demonstrating. 



Relative Transpiration in Cacti: Dr. Bxjr- 

 TON Edward Livingston, Desert Botan- 

 ical Laboratory. 



After a preliminary discussion of the 

 meaning of relative transpiration, i. e., the 

 ratio of the increment of water-loss from 

 the plant for any time interval to the cor- 



