OF INFLORESCENCE. 25 



base of each flower — as Pitcairnia. Of these bracts, 

 the lower one represents the true leaf; the two others 

 are the bracteoles of a very short peduncle, and the 

 whole forms a Spiciform Thyrse. In neighbour- 

 ing species we see these peduncles elongated into 

 true cymes. 



Lastly, we have seen, in speaking of Cymes, that their 

 branches seem, from the abortion of one of them, to 

 bear lateral flowers : when this phenomenon is combined 

 with that which I have mentioned, there results a sin- 

 gular kind of inflorescence, which may be seen in the 

 woody kinds of Echium ; the axis lengthens indefinitely 

 by its summit, and bears branches laterally, which arise 

 from the axils of leaves changed into bracts. These 

 branches are true c\mes, reduced by abortion to only 

 their terminal flowers which appear lateral, or scorpioid 

 cymes ; the whole then is a thyrse with scorpioid cymes, 

 or, if we wish, for the sake of abbreviation, a Scorpioid 

 Thyrse. 



Thus, Thyrses are systems of inflorescence, of which, 

 1st, the central axis follows the laws of indefinite inflo- 

 rescence, and may present all its modifications, such as 

 the states of spikes, elongated corymbiform racemes, 

 umbels, &c. ; and of which, 2d, the lateral branches 

 follow the laws of terminal inflorescence, and may pre- 

 sent all its modifications, viz. the state of dichotomous, 

 trichotomous, scorpioid cymes, fascicles, and glome- 

 rules. The evolution of these two systems follows the 

 laws of each : — the development of the central axis and 

 its parts proceeds from the base upwards ; that of each 

 of the lateral branches commences at the centre and 

 follows a centrifugal course. 



