BIOLOGY. 329 



conducted at Woods Hole at the request of the Bureau of Fisheries, 

 which are still being carried on. After several years of collecting and 

 research, it seemed to be proper to emphasize by this report the great 

 economic value of a thorough and continuous study of the diatom flora 

 of the coastal waters, because of the importance of these plants to the 

 feeding and the abundance of our edible sea-fishes. The variation in 

 the quantity of marine diatoms in different years and at different 

 seasons of the year, coupled with the variation in the quantity of migra- 

 tory fishes at different parts of the coast, was discussed; the relative 

 value as fish-food of different kinds of diatoms was treated, and the 

 important question was raised as to the possibility of controlling to 

 some degree the quantity and quality of the diatom flora at such points 

 along our seaboard as are best adapted to the capture and transporta- 

 tion of marketable fish. The writer ventured the opinion that this 

 highly important control of fish food was distinctly possible. 



Morgan, T. H., Columbia University, New York. Study of the constitution 

 of the germ-plasm in relation to heredity. (For previous reports see Year 

 Books Nos. 15-18.) 



The follo'wing report covers the work of T. H. Morgan, C. B. Bridges, 

 and A. H. Stm'tevant, for the year 1919-1920, on the constitution of 

 the hereditaiy materials of Drosophila, earned out at the Zoological 

 Laboratoiy of Columbia University and at the Hopkins Marine Station 

 of Stanford University. 



The maps of all four chromosomes of Drosophila melanogaster are be- 

 ing improved, both by locating more accurately already known mutant 

 genes and by finding and placing new genes. The work has progressed 

 so far that a revision of the first and second chromosomes has become 

 necessary, but before undertaking this it is proposed to publish all 

 available data concerning the third and fourth chromosomes. 



A few examples will serve to show the nature of the improvements 

 that are being made in the maps. The third chromosome has been 

 lengthened at both ends — 25 units to the left by the discovery of rough- 

 oid and 9 to the right by minute and claret. The improvement in the 

 map of the second chromosome has consisted mainly in filHng in regions 

 where no genes or poorly workable genes were previously known. For 

 example, two new useful dominants, "gull" and "lobe," have been found 

 and the large gap between curv^ed and arc has been filled by two 

 mutants, a dominant (minute-2) and a recessive ("humpy"). 

 The discovery of a new gene, cross veinless, in the first chromosome, 

 lying in the gap between ruby and cut, fills up the chromosome so 

 that we are now able to study any region of the X-chromosome with- 

 out the occurrence of unobserved double crossmg-over. In our first 

 report 36 mutant genes in the first chromosome were recorded; at the 

 present writing we have met with and examined about 125 mutant genes 

 in this chromosome. In the fourth chromosome the attempt to obtain 



