SECRETIVE TISSUES. 



141 



A microscopic examination of the anatomy of nectaries 

 shows them to be composed of small cells closely resembling 

 the merismatic condition of ordinary cellular tissue (see 

 Fig. 43, a), and similar to the arrested parenchyma of the 

 pulvinus at the base of the petiole of sleeping leaves, which 

 enables that organ to remain flexible. Or, again, it is very 

 similar to the conducting tissue of the style, which owes its 

 origin to the irritating effect of the pollen-tubes (chap, xviii.). 



The function of the nectary is to secrete honey, or, to 

 speak more accurately, either principally glucose, or else cane 

 sugar, or both, for the proportion varies greatly.* 



The position of nectaries in flowers is very various, and any 

 organs can form them. It will be enough to enumerate a few 

 localities as follows : The Lime, species of Malpighia,i and 

 perhaps Coronilla, furnish instances, which are comparatively 

 rare, of the sepals of the calyx being 

 nectariferous. In Buttercups, Hellebore, 

 and Aconite, nectar is secreted by the 

 petals or their representatives. In 

 Violets, Atragene (Fig. 44), Fentstemon, 

 and Stellaria the filaments undertake 

 the duty, while in Caltha, Monotropa, 

 and Rhododendron it is the carpels or 

 pistil. In most instances the honey is 

 secreted by glands, disks, etc., issuing 

 out of the floral receptacle. If the ovary Fig. 44.-Petais passing into 

 be inferior, then the secreting structure T^j^^^a^ter Ser). '" 

 is on its summit, as in the Tlmhelliferce ; 



and in that case it is the base of the styles from which the 

 nectariferous tissue is developed. 



The Origin of Nectaries. — Limiting one's self to those in 



* Bull. Soc. Bot. Fr., viii. (1886), Rev. Bibl, p. 212. 

 t Nature, vol. xvii., p. 78. 



