46 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



TERMINOLOGY. 



The morphological nature of the bur characteristic of Cenchrus 

 seems not to have engaged the attention of botanists until recent 

 years. In his description of the genus Linnaeus refers to the bur 

 as an involucre ; in the Species Plantarum " female glumes " is the 

 term used for bur, as shown by the description of G. tribuloides 

 "glumis femineis globosis muricato-spinosis hirsutis." The great 

 majority of authors, early and late, have used the term involucre or 

 involucel, common involucre, or involucre of spines. Ray uses the 

 word " echinus," which is about the equivalent of our word " bur." 

 Sloane writes of the " little burs or large roundish prickly seeds." 

 Morison and Scheuchzer use the term "locusta" for the bur, ap- 

 parently regarding it as a spikelet, since locusta is the term in com- 

 mon use by early authors for spikelet. Adanson describes the bur 

 under calyx; Cavanilles calls it a common calyx. Trinius at first 

 uses the term " capitulus " and later the same word for the bur of 

 G. tribuloides and " involucel " for that of G. myosuroides. Hackel 

 uses the word " Hiillen," envelope or husk. Several authors have 

 used the terms bur or false capsule (Scribner, Wooton and Standley) 

 as well as the term involucre. Nash describes the bur as consisting 

 of " two spine-bearing valves forming a bur " (in several species, espe- 

 cially in G. fauciflorus, there is a deep cleft on the outer face of the 

 bur). In none of these usages is there any indication of what the 

 bur is supposed to be morphologically. 



Doell 1 suggests that the involucre is derived from a leaf. He 

 states [translated] : 



At the base of the spike of C. tribuloides and other species of this genus are 

 often to be seen rudimentary bracts, from the axils of which spring branches 

 provided with an involucre at base ; this appears to me noteworthy. I suspect 

 that the involucre itself has perhaps been formed from a many-cleft bract on 

 the common axis. The nature and structure of the involucre will be discussed 

 in another place. It is enough to say here that the involucre of Cenchrus has 

 been derived from a single leaf. 



The bract mentioned is that visible at the base of most panicles of 

 grasses, usually represented by a minute ridge. The lowest bur of 

 the spike in this genus is sometimes abortive, appearing as a narrow 

 fascicle of bristles. Such an aborted bur must have been the branch 

 that Doell observed in the axil of the bract. 



Goebel, 2 as the result of a study of the development of the inflor- 

 escence of Cenchrus echinatus and G. spinifex, shows that Doell's con- 

 clusion was erroneous and that, instead, the bur is derived from co- 

 hesion of the members of a complex system of branches. This theory 

 accords perfectly with observations made by the author. 



x In Mart. Fl. Bras. 2 2 : 309. 1877. 



' Jahrb. Wiss. Bot. Pringsh. 14: 21-23. 1882. 



