UNUSUAL DICHOTOMOUS BRANCHING IN VERNONIA.* 



John H. Schaffner. 



During the summer of 1918, the writer observed a remark- 

 able occurrence of dichotomy in the stems of the ironweed, 

 Vernonia baJdwinii Torr. {Vernonia interior Small). Large 

 numbers of stems were found that had a perfect dichotomy 

 occurring at various heights from the ground to near the top of 

 the inflorescence. The writer has observed isolated, individual 

 cases of such two-forked branching or twinning in other plants, 

 as for exemple in the inflorescence of Chcctochloa viridis (L.) 

 Scrib. and Lacinaria punctata (Hook.) Ktz. But such examples 

 have been exceedingly rare. 



Since the study of abnormal developments has received a 

 new importance in practical investigations on heredity, it was 

 thought worth while to make a record of the facts observed. At 

 Morganville, Clay County, Kansas, several hours of superficial 

 search along two ravines for about a mile resulted in the dis- 

 covery of 81 such stems, mostly belonging to different individual 

 plants. This Vernonia is a crown-former, sending up a number 

 of shoots each year which are usually unbranched below the 

 inflorescence unless injured, when abundant branching occurs 

 of the usual monopodial type from buds in the leaf axils. The 

 shoots are usually from 1 — 6 feet high and the inflorescence is 

 much branched. 



The division of the bud begins by a widening of the stem 

 which soon becomes grooved on the two sides and after some 

 inches of this double or twin structure gives rise to two usually 

 separate branches. It is rather difficult to observe the plants 

 rapidly because the dichotomous shoot may be hidden by 

 neighboring, normal ones but the abnormality is nevertheless 

 very striking. Only one clump was found in which all the stems 

 were dichotomous and this individual had but three shoots. 

 Usually one or occasionally two shoots are dichotomous in a 

 clump. Sometimes a shoot is forked a second time above 

 either in one or both branches and it is interesting to note that 

 in all such cases found the second dichotomy is at right angles 

 to the first. 



* Papers from the Department of Botany, The Ohio State University, No. 110. 



487 



