258 PHYSIOLOGICAL BOTANY. PART II. 



the calyx and corolla serve, of protecting the stamens 

 and pistils in the early stages of their development, 

 they occasionally perform a similar office at a later 

 period in protecting the seed. In some cases they 

 remain attached to the seed-vessel in the modified 

 form of membranous or chaffy appendages, which 

 serve as sails to waft the seed to a distance. Some 

 of the most familiar and effectual contrivances of this 

 description are to be seen in the Composite? ; such 

 as the common dandelion and thistles. In these cases 

 the down attached to each seed is only a modified form 

 of the calyx. 



(253.) Functions of the Nectary. As the nectary 

 has been noticed in not fewer than seventy-two families, 

 and is found in a vast number of species, its use is 

 probably of some importance in the general economy of 

 reproduction, though we do not know what this may 

 be. The most plausible conjecture that has been 

 offered supposes the secreted matter or nectar to be 

 discharged by the organ on which it is seated or 

 near which it is placed, whilst it is elaborating the 

 juice for the use of the inner whorls. An important 

 secondary purpose which it serves is to allure bees and 

 other insects, which crawling over the flowers, and pass- 

 ing from one to the other, facilitate the dispersion of 

 the pollen, and thus promote the fertility of the plant 

 in the waywe are about to mention under our second 

 period. 



(254.) Development of Caloric. At the time of the 

 flower's expansion a considerable development of heat 

 takes place in certain species, and there is also a rapid 

 formation of carbonic acid. This phenomenon is most 

 strikingly exhibited by some of the Arum tribe. The 

 spadix of the common arum (Arum maculatum) at- 

 tains a temperature of 7 R- or 47f Fahr. above that 

 of the atmosphere, and the Arum cordifolium in the 

 Mauritius has been observed to attain a temperature of 

 44 to 49 R. or 131 to 142^ Fahr. that of the sur- 

 rounding air being at 19 R. or 74 J Fahr. These 



