D. J. SCOURFIELD OX MENDELISM AND MICROSCOPY. 413 



depend upon microscopic .structures, these being sometimes simple 

 and sometimes compound. A very good case in point is to be 

 found in the colours of stocks (Matthiola), which have been 

 studied by Miss Saunders. In the course of her experiments 

 four main types of coloration were observed — white, cream, red 

 and purple* (uniformly coloured), and red and purple (with 

 cream eye). These naked-eye characters were found to be pro- 

 duced as follows : the whites had colourless cell-sap and colourl- 

 corpuscles or plastids in the cells; the creams had colourless cell- 

 sap and coloured (yellow) plastids; the uniformly coloured reds and 

 purples had coloured cell-sap and colourless plastids ; and, lastly, 

 the reds and purples with cream eye had coloured cell-sap and 

 coloured plastids. The experiments started with crosses between 

 whites and creams, and the hybrids produced were all uniformly 

 coloured purples, showing (1) that the coloured were recessive to 

 the colourless plastids, a fact in itself sufficiently remarkable, as 

 it has the appearance of a negative dominating over a positive 

 character ; and (2) that a coloured cell-sap was produced — i.e. 

 an altogether new character appeared. The explanation of the 

 latter phenomenon does not concern us in this connection f ; but 

 it must be observed that the production of the coloured cell-sap 

 was not dependent in this instance merely upon the meeting of 

 the coloured and uncoloured plastids, for they both occurred 

 associated with either colourless or coloured cell-sap. The next 

 generation gave rise not only to whites, creams, and uniformly 

 coloured reds and purples, but also to the fourth type already 

 mentioned — i.e. to reds and purples with cream eye, which were 

 due to the reappearance of the recessive yellow plastids in 

 association with coloured cell-sap. 



There are undoubtedly many similar cases to the one just 

 quoted, in which the naked-eye appearances are due to more or 

 less complex associations of microscopic colour factors. One such 

 occurs to me amonsr the Entomostraca. When in Scotland a few 

 years ago, making observations on this group of animals in con- 

 nection with the Lake Survey, I found in Loch Tarff, near Fort 

 Augustus, specimens of Liaptomus laticeps, Sars, which, to the 



* The purple colour is due to an independent factor superimposed on 

 the red. 



f For the latest views on this and similar results, see Report III. 

 to the Evolution Committee of the Royal Society, 1906. 



