156 



THE STOKY OF THE PLANTS. 



it has below it what seems at first sight to be a 

 big green calyx of very numerous sepals. What 

 is this deceptive object ? Well, it is called an 

 involucre, and it really acts to the compound 



flower-head very 

 much as the calyx 

 acts to the single 

 blossom. The 

 florets having got 

 rid of their sepa- 

 rate calyxes, the 

 flower-head pro- 

 vides itself with 

 a cup of leaves 

 (technically called 

 bracts), which pro- 

 tect the unopened 

 head in its early 

 stages, and serve 

 to keep off ants 

 or other creeping 

 insects exactly as 

 a calyx does for 

 the single flower. 

 Inside this invo- 

 lucre, again, all 

 the florets of the 

 thistle are equal 

 and similar. Each 

 has a tiny calyx, 

 hardly recognis- 

 able as such, made up of feathery hairs which 

 cap the inferior ovary. Within this fallacious 

 calyx, once more, the floret has a purple corolla 



TIG. 36. FLOWER - HEAD OP A 

 THISTLE, CONSISTING OF VERY 

 NUMEROUS PURPLE FLORETS, 

 ALL EQUAL AND SIMILAR. 



