18 



THE AMEBIC AX NATURALIST [Vol.LYI 



extent or not at all through the pollen— to less than 2 per 

 cent, in a large series of crosses. 



The next mutant found was Cocklebur (3, fig. 11) 

 named from the resemblance of its fruits to those of the 

 cocklebur weed. The plant is weak and lopping and the 

 leaves narrow and twisted. 



The Poinsettia mutant (3, fig. 14) was named from a 

 fancied resemblance of its long clustered leaves to the 

 hothouse plant of that name. The Poinsettia is of espe- 

 cial interest, since this mutant was found to give curious 

 ratios when heterozygous for color factors. 



As our eyes became better trained, other mutants were 

 added to the list, largely through the keen discrimination 

 of Mr. Avery and Mr. Farnham, until we now have 12 

 main mutants with some varieties, all of which transmit 

 their mutant characters essentially in the same way in 

 which the Globe complex was found to be transmitted. 



In addition we had a mutant which, unlike the 12 types 

 just mentioned, was found to breed true, and since it is 

 practically impossible to obtain crosses between it and 

 the normal form from which it arose, it was called " Xew 

 Species " (3, fig. 15). The capsules are somewhat spheri- 

 cal and the leaves broad, although in a race of the same 

 type later discovered the leaves are not greatly different 

 from the normals. Heterozygous plants of the " N". S." 

 sometimes gave curious ratios in their ofifspring. 



Such was the situation up to the spring of 1920, when 

 we were fortunate in securing the cooperation of Mr. 

 Belling in a study of the nuclear condition of our mutants. 

 On the basis of his work we are able to make the classi- 

 fication of types showTi in Fig. 2. In the individual fig- 

 ures -which of course are highly diagrammatic— the 

 chromosomal constitution of somatic cells is represented. 

 We have not attempted to represent the size differences 

 determined by Mr. Belling and i^ietured in our pa])or in 

 the morning session.' A woi-d ol" <'xi)l;iiuitiou of terms 

 is desirable. The terms (liploid, triploi.l and t.'l rai)l.)id 

 are already current to indicate a balanced condition in 

 which each chromosomal set {we can not say chromosomal 



