March, 19 19, The Irish Naturalist. 25 



HETEROCARPY IN PICRIS ECHIOIDES. 

 by george h. pethybridge, b.sc, ph.d. 



(plate 3). 



Heterocarpy is the term employed for describing the 

 condition which arises when one and the same species of 

 plant produces in the same individual two or more distinct 

 and different types of fruit. 



The subject is not one which is dealt with, as a rule, 

 in botanical text-books, and the literature on it, although 

 fairl}^ considerable in amount, is somewhat scattered and 

 not always very accessible. A short list of the more 

 important relevant papers is appended to this axticle ; and 

 further bibliographical references will be found in the 

 papers referred to. 



The principal families in which heterocarpy is known to 

 occur are the Compositae, the Chenopodiaceae and the 

 Cruciferae ; while in some of the Umbelliferae we have 

 examples of heterocarpous mericarps. 



Picris (Helininthia) echioides — tlie Bristly Ox-tongue — 

 one of the Compositae, is not a common plant in Ireland. 

 In Praeger's Topographical Botany it is recorded from 

 only seven County divisions and is regarded as a possibly 

 introduced species. Its seeds (in reality one-seeded fruits) 

 are sometimes found as impurities in cLgixcuiuuitxi seeds 

 imported into the country, chiefly in clovers of Italian 

 origin. The plant is mentioned, and what may, perhaps, 

 be termed its normal fruit is illustrated, in Johnson and 

 Hensman's paper ^ on Agricultural Seeds and their Weed 

 Impurities. 



This normal fruit is more or less cylindrical or slightly 

 flattened and has transverse wrinkles on its surface which 

 are more prominent towards its upper end. Its somewhat 

 contracted top passes into the stalked, plumose pappus 



^ Sci. Proc. R. Dublin Soc. xii. (n. s.) no. 33. July, 1910, p. 455, 

 and PI. xxiii., Fig. 44. 



A 



