No. 554] SHORTER ARTICLES AND DISCUSSION 



121 



throw off variants that in taxonomic practise would be consid- 

 ered new species readily distinguished from the parents of the 

 cross and from the F 1 hybrid. I have this past summer found 

 that F 2 hybrids similar in character to the F, will in the P, 

 generation repeat the performance of the F 2 and throw off again 

 some of the same marked variants. 



It is a satisfaction to know that De Vries and Stomps stand 

 firmly by the original definition of a mutation as a germinal 

 variation (and this means inheritable) from a pure stock, i. e., 

 from homozygous material. This is a valuable concept whether 

 or not mutation proves to be a rare phenomenon. Furthermore, 

 one of the most important lines of experimental study is that 

 which will endeavor to determine with precision the conditions 

 under which true mutations may arise. There has been a loose 

 usage of the term mutation which should it become prevalent will 

 take from the word the significance described above, and reduce it 

 to a meaning no more precise than that of a marked germinal 

 variation from any source. If the word mutation is to be kept in 

 the sense of De Vries it must be reserved for germinal variations 

 from homozygous stock. 



Bradley Moore Davis 



A CONVENIENT MICROSCOPE CASE 

 A very convenient case for holding microscopes, especially for 

 large, beginning courses where two or more students in different 

 sections use the same instrument, is shown in the accompanying 

 photograph. 



The case here shown was built to stand in a shallow offset in 

 the laboratory near a door, and fills a small space that would 

 otherwise be wasted. As is seen from the numbers below the sec- 

 tions, it will hold fifty standard microscopes. Each instrument 

 has a number on the base to correspond to the number on its re- 

 spective section. Across the floor of each section, at the back, is 

 nailed a 2 in. X 2 in. strip of wood to stop the base of the micro- 

 scope and to serve as a shelf for the extra oculars. Holes of the 

 proper diameter in the shelf would hold these oculars more 

 safely. The doors slide easily on a metal track with ball-bearing 

 wheels and have brass pushes set flush with the surface of the 

 wood. They may be fastened with a catch or with a lock and 



