INFLORESCENCE. 



71 



blossoming commences with the central flower and proceeds in order 

 to the circumference, as in the sweet-william, elder, hydrangea. 



In this kind of inflorescence all the flowers are considered terminal because they 

 do in fact (except the first which terminates the axis) terminate lateral branches 

 successively produced on a definite plan at the node next below the primary flower. 



344. Both kinds op inflorescence are occasionally combined in iho same 

 plant, where the general system may be distinguished from the partial clusters 

 which compose it. Thus in the Compositss, while the florets of each head open 

 centripetally, the general inflorescence is centrifugal, that is, the terminal head is 

 developed before the lateral ones. But in the Labiate the partial clusters (verticil- 

 asters) open centrifugally while the general inflorescence is indefinite, proceeding 

 from the base upwards. 



345. Of centripetal or axillary inflorescence the principal 

 varieties are the spike, spadix, catkin, raceme, corymb, umbel, pani- 

 cle, thyrse, head. 



346. The spike is a long rachis with sessile flowers either scattered, 

 clustered, or crowded upon it, as plantain, mullein, vervain. The so- 

 called spikes of the grasses, as wheat, timothy, are in fact compound 

 spikes, bearing little spikes or spikclets in place of single flowers. 



347. The spadix is a thick, fleshy rachis with flowers closely sessile 

 or imbedded on it, and usually with a spathe, as in the Arum, or with- 

 out it, as in the Typha. 



200, Spiranthes cernua; flowers in a twisted spike. 201, Orontium aqnaticum ; flowers on a 

 Daked spadix. 202, Betula lenta; flowers in aments. 



348. The catkin or amentum is a slender, pendant rachis with scaly 

 bracts subtending the naked, sessile flowers, and usually caducous, as in 

 birch, beech, oak, willow. 



349. The raceme is a rachis bearing its flowers on distinct, simple 

 pedicels. It may be erect, as in hyacinth, Pyrola, or pendulous, as in 

 currant, blackberry. 



