Apbil 3, 1908] 



SCIENCE 



541 



individual from the fertilized egg is a matter 

 of the assimilation of food and the conversion 

 of food materials into tissues; and that if we 

 imderstood all the metabolic processes that 

 occur in the body we might possibly be able 

 to understand why a given egg develops into 

 a specific organism. At present we do not 

 kaow a great deal about the exact locality in 

 which various processes occur or the cause or 

 nature of the changes which do occur, but 

 there are reasons to believe that the chromatin 

 is of highest importance in assimilatory proc- 

 esses. The cytoplasm also, at least in some 

 of the cells of the body, must also take an 

 important part. Inheritance is easier to un- 

 derstand than development. The gamete, 

 composed of certain substances built into more 

 or less definite structures, is so organized that 

 by assimilation of food the cell is able to 

 reproduce itself. Important differences fre- 

 quently appear when we pass from one gen- 

 eration to the next. 



1. One of the most important, and by far 

 the most common cause of variation, lies in 

 the new groupings of hereditary characters 

 which occur when two gametes unite, the 

 preparation for the new grouping having been 

 made in the formation of the gametes. Any 

 definite structures in the cell which have im- 

 portant functions in the metabolism of food 

 and which retain their identity in passing 

 from one cell to another may determine im- 

 portant differences between parent and off- 

 spring. The facts of Mendelian inheritance 

 indicate that there are such definite structures 

 which become rearranged with the production 

 of new gametes and their subsequent union. 

 We may include here all variation due to re- 

 combinations of Mendelian unit characters. 



2. The definite structures of the cell, which 

 because of their composition bear definite rela- 

 tions to metabolic processes, may, by change 

 in composition or in environment, change in 

 their relation to the metabolic processes. 

 Speaking in a general way, the development 

 of the numerous varieties of domesticated 

 species seems to have arisen from the loss of 

 functions formerly possessed by definite struc- 

 tures within the cell, perhaps in the main the 

 chromosomes. The author, to gupport this 



supposition, gave illustrations of the variation 

 in color in domesticated hogs, and called at- 

 tention to de Vries' application of the same 

 theory to explain the origin of the numerous 

 varieties of cultivated plants. 



3. New functions may be acquired by ceU 

 organs causing new characters to appear. It 

 is supposed that evolutionary progress in the 

 main is of this character. Such changes may 

 be slow and gradual or instantaneous. 



4. Change of environment may cause 

 marked changes, as in the case of the cassava 

 plant, which loses its prussic acid when 

 brought from the tropics to Louisiana. Hard 

 wheat taken to the Pacific coast becomes soft 

 in a few years. Champion tomatoes from 

 seed grown in Pennsylvania produce Cham- 

 pion tomatoes in Louisiana, but the seed pro- 

 duced in Louisiana yield a very different type 

 of tomato. These variations are probably due 

 to changes in metabolic activities, perhaps in 

 the chromatin and in the cytoplasm. Such 

 changes may be reversible or not. This par- 

 ticular phase of variation offers to the student 

 an inviting field in which too little work has 

 been done. 



5. Loss or gain of chromosomes resulting 

 from accidents in cell division may cause im- 

 portant variations. Recent investigation in- 

 dicates that we may find here an explanation 

 of the so-called mutations of de Vries. 



Professor Spilknan's paper was followed by 

 a prolonged discussion. 



The second paper, "A Eoot Disease of 

 Tobacco," by Mr. W. W. Gilbert, was an 

 account of the disease caused by the fungus 

 Thielavia hasicola, which is the subject of a 

 forthcoming bulletin of the Bureau of Plant 

 Industry. 



Under the title " Some Peculiar Seedlings " 

 Professor J. B. S. Norton described a series 

 of experiments in germinating immature seeds 

 of the cowpea. From the time of fading of 

 the flowers he collected seeds at intervals of 

 three days. He found that those which were 

 three weeks from the seed, about one tenth 

 normal size, sprouted and produced slender 

 but normal plants. 



Mr. J. H. Painter, of the United States 

 National Museum, then gave an account of 



