1 1 2 D. J. SCOURFIELD ON MENDELISM AND MICROSCOPY. 



axis, which, however, does not extend to the margin. Wrinkled 

 peas, on the other hand, contain starch in grains of a more circular 

 type, with four, five, or more notches on the edge, which repre- 

 sent the points where internal radiating fissures reach the margin. 

 These grains may eventually break up along the lines of the 

 fissures, and the starch is then seen in the form of minute 



'ments of circles. The " roundness " and " wrinkleclness " of 

 peas is, therefore, really the outward expression (more or less 

 imperfect, owing to various external causes) of a more funda- 

 mental difference connected with the condition of the starch ; and 

 the category to which any particular pea belongs can always 

 be settled by an examination of the starch grains it contains. 

 Hybrids between round and wrinkled races are found to exhibit, 

 as their shape would indicate, only starch grains of the pure 

 round type. Strangely enough, until the recent experiments 

 undertaken to test Mendel's results led to an investigation of 

 the matter, none of the specialists on starches seemed to have had 

 any notion that pea-starch might be of two such radically distinct 

 types. It is another illustration of the remarkable way in which 

 new facts, about what are supposed to be hackneyed subjects, 

 are brought to light by means of new working hypotheses, 

 whether right or wrong. There is probably still a great deal 

 to be learnt about the relation of starch grains to the external 

 character of seeds of all kinds, and their systematic investigation 

 from this point of view would be a task well worth taking up. 



Another example of the connection between microscopic and 

 macroscopic characters, from the standpoint of Mendel's law, is 

 to be found in the pollen of certain plants, although in this case 

 the naked-eye characters do not depend directly upon the minute 

 structures referred to. In one of the varieties of sweet peas 

 (Lathyrus), known as " Emily Henderson," pollen grains of two 

 different forms are found — namely, round with two pores, and 

 long with three pores. There is no visible difference in the 

 plants bearing these, both producing white flowers ; but when 

 they are crossed they always give rise to plants with coloured, 

 mostly purple, flowers. The two kinds of pollen grains, there- 

 fore, evidently indicate strains of plants of an unsuspected 

 complexity in their differences. It may be added also that 

 the long pollen behaves as a dominant to the round pollen. 



Again, the colours of plants and animals very commonly 



