BRACTS AND FLOEAL LEAVES. 



79 



above described. Thus there are compound racemes and corymbs, 

 where the branches of highest order are themselves racemes and 

 corymbs. If the branching is irregular, a panicle is the result. 

 The large group of UmbelliferaB is characterized by the occur- 

 rence of umbels, usually compound. Hence the name. Carrot, 

 parsnip, hemlock, and the like are examples. Bracts may be 

 absent or form a general involucre round the origins of the 

 primary branches, and partial ones where the branch or par- 

 tial umbels arise. Compound spikes occur in many grasses. 

 It does not always happen that the branching is of the same 

 kind throughout. Thus, in grasses, the spikelets (i.e., small 

 spikes) are not always arranged in compound spikes, but may be 

 in racemes or panicles. 



Cymose or definite inflorescences branch in the way already 

 described on p. 24. They are called " definite " because the main 

 axis after producing a flower at its end ceases to elongate, and 

 is overtopped by its branches, which grow in the same manner. 

 Simple and compound cymes may be distinguished. Taking the 

 former first, a subdivision may be made into forms where a 

 pseudaxis or sympodium is (1) absent, (2) present. The false 

 dichotomy of mistletoe (p. 4) exemplifies the first kind, and so 

 do the dichotomous or two-rayed cymes of campion and stitchwort 

 (cf. fig. 35), where, however, the end of the main axis is of fair 



fig. 



-Forked Cyme. 



FIG. 36.— Helicoid Cyme of 

 Forget-me-not. 



length, and bears a flower, so that the forking is obviously due 

 to lateral branches. The central flower opens first, then those 

 terminating the first pair of branches, and so on. For this 

 reason cymose inflorescences have been called centrifugal. A 



