INFL0BB8CSNCE. 



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 coQsiderod 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 of infloeesoesce are occasionally combined in tlie same 

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

 which compose it. Thus in the Compositse, 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 Labiatce the partial clusters (verticil- 

 asters) open oentrifugally 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 spikelets 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 spathc, as in the Arum, or with- 

 out it, as in the Typha. 



MO, Splranthoa ccrnns ; flowers in a twisted spike. 201, Orontlam nquaticum ; flowers on a 

 nailed spadix. 202, Betnla lenta; flowers in amcnts. 



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. 



