VARIATION IN TITHYMALOPSIS 



J. B. S. Norton 



Maryland Agricultural College 



In studying the species of Euphorbiaceae around Washington, 

 D. C, for the District Flora, it became necessary to determine 

 more carefully the status of the species of Tithymalopsis found 

 there. T. corollata (L.) Klotsch & Garcke and T. Ipecacuanhae 

 (L.) Small, both generally recognized as very variable species, are 

 very common in this region, and in recent years two others, T. 

 arundelana (Bartlett) Small and T. marylandica (Greene) Small, 

 intermediate between the other two, have been described and rarely 

 found. 



In analyzing the plants of these species found this year I have 

 plotted the characters of all the plants seen (over 400) in the 

 accompanying tabulation which I think will show the relation of 

 the several species and the relative number of each conspicuous 

 variation in the total population. I would like to commend to 

 others the method of analysis of variable species which I have used, 

 as an easy means of forming a clear picture of the above relations. 



The plants studied have not been selected entirely at random, 

 though mostly so, and the more unusual kinds will appear a little 

 more frequent in the tabulation than they should by chance. 



The progressively subdividing arrangement of the tabulation, 

 allowing for all possible combinations of the variable characters, is 

 explained in the following notes: The first column divides the 

 plants on whether a distinct white appendage is present or not 

 on the involucral glands. All of typical T. Ipecacuanhae is in- 

 cluded in the "appendages none" group, though on almost every 

 one of the hundreds I have seen, there is a narrow appendage easily 

 seen with a magnification of 10 diameters. I might also add here 

 that every specimen of any species of Tithymalopsis which I have 

 examined has distinct, though minute, stipules. 



The second column includes under "none" those forms where 

 the first cyathium arises from the ground or below. The short- 



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