THE MUTATION THEORY. 



179 



flowers. Striping appears only after the white or yellow variety has 

 acquired complete purity, i.e., after a number of generations. The 

 striping, therefore, exhibits a tendency to revert to the original colour. 



As an example of a proliferous plant Professor de Vries experimented 

 with Plantago lanceolata ramosa. He found that 50 per cent, of the 

 offspring came more or less true, the rest reverting to the natural condi- 

 tion. He adds that " the number of compound ears per plant, and the 

 degree of branching in each, are to a great extent dependent on the con- 

 ditions of life. The stronger the growth of the whole plant, and the 

 richer the foliage, the more pronounced will the anomaly be. . . The 

 young plants almost always begin with unbranched ears ; it is not until 

 later that the monstrosity appears, gradually increasing in strength." 

 Such appears to be the rule with all, even when the abnormality arises 

 from some impoverishment, as some double flowers do; subsequently, 

 however, high cultivation intensifies it. With regard to composites, 

 we have a very instructive account of the origin of a true double corn 

 marigold in the author's experiments. The wild form has 13 ray 

 flowers, but under cultivation that number has been increased to 21 and 

 34. This he raised to 49, 67, and about 90, in three years successively. In 

 all these the lignlate florets only increased in number on the circum- 

 ference ; then two or three such appeared in the midst of the disk florets. 

 This was the first indication of the true double race which was fully 

 developed in the next four years by selection. An interesting phyllo- 

 tactical feature comes out when the number becomes high. The three, 

 or we may say four, " cyclical " numbers, 8, 13, 21, 34, prevail. These 

 form the well-known cycles " on the different and successive angular 

 divergences f, -^j, ff . The next numbers ought to be 55, 89, 144," 

 &c. But the number of florets cannot advance quite so rapidly; for 

 Professor de Vries found that from 1895 to 1897 it only rose from 21 to 34 ; 

 then in 1898 it reached 48; in 1895, 66; and in 1900 to 101. It 

 showed a ' * determination " to go on increasing, though unable to rise at 

 once to 89 and 144. The new additions appeared irregularly among 

 the disk florets. Another feature is that when plotted in curves the 

 maxima advance. Thus in 1892 there were two (normal), viz., 21 and 

 34; in 1898 there were three, 26, 34, 48: 34 alone being normal; in 

 1899 to this were added 45, 47, and 66. Lastly, m 1900 the tallest " 

 maximum was 47 and another reached to 101. Some of these addi- 

 tional " cyclical " numbers may, perhaps, be partially accounted for 

 as combinations of others. Thus 26 ^--5 + 8 + 13, or 2 x 13 ; 47 = 34 -f 13 ; 

 50 = 34-f 13 + 3; 58 = 55 + 3, &c. But this must be taken as hypothe- 

 tical only. 



Experimenting with the pelorian form of Linaria vulgaris, Professor 

 de Vries tried to verify Hofmeister's assertion that the " origin of 

 profound deviations from the normal form ... of monstrosities " 

 was " sharp and sudden." He cultivated the Toadflax for seven years, 

 when "the peloria appeared quite suddenly in the fifth and sixth 

 generations. " 



It may be observe'd that the spur is an " enation," growing after 



