324 REPORT UPON COTTON INSECTS. 



cherrima (PL III, Figs. 7-10), the flowers are collected into clusters consist- 

 ing of a central, stalked, pistillate flower, surrounded by a varying 

 number of stalked monaiidrous staminate flowers, the whole cluster being 

 inclosed in an involucre so as to resemble somewhat a single flower. On 

 the side of each involucre is a large, yellowish, cup-shaped gland, which 

 secretes a considerable quantity of nectar during the blooming period of 

 the cluster to which it belongs. In the house this is sought by myriads 

 of the small red ant Myrmica molesta, and in the open air of its native 

 place probably by small bees and flies such as are known to visit other 

 Euphorbias. When one of these clusters begins to expand the pistillate 

 flower at its center is protruded (PL III, Fig. 8, o), and expands its three 

 bilobed stigmas, which are ready for fecundation. A few days later, 

 these having withered, the stalk of the pistillate flower becomes suffi- 

 ciently elongated to protrude the entire ovary * (PL III, Fig. 7, o), and by 

 this time several of the stamens have become exserted and shed their 

 pollen. From this it appears that in this species self-fertilization is im- 

 possible, since there are no perfect flowers; the first remove from this, 

 crossing between flowers of the same cluster, is likewise impossible, 

 owing to the maturing of the pistillate flower before any of the stamin- 

 ate flowers are mature; and the closest cross that can occur is between 

 different clusters on the same plant, which, as appears from the crowded 

 structure of these clusters, is about equivalent to crossing different 

 flowers on the same plant of such a species as the Marcgravia figured, 

 for a number of these involucrate clusters are collected together and 

 surrounded by a whorl of bright crimson bracts, rendering the whole 

 very conspicuous to such insects as are in search of nectar. These in- 

 sects, in obtaining the nectar, necessarily brush the floral organs and 

 must secure the cross-fertilization of the species. 



Another example of nectar borne on a floral involucre is afforded by 

 the cotton plant, where each flower is surrounded by a whorl of three 

 large laciniate bracts, on the outside of each of which, near its base, is 

 a nectariferous pit.t 



Alternating with these bracts, and just within the circle formed by 

 their bases, are three other pits, smaller than the former, but like them, 

 active.} 



The first few flowers that open possess only rudiments of glands; but 



*In cultivation the pistillate flower is often entirely abortive (Figs. 9 and 10), and 

 its ovules seem to be always aborted in onr greenhouses, for though an abundance of 

 apparently good pollen is produced I cannot learn that the species ever set seed \vith 

 us. My authority for this failure to set seed is Peter Henderson, the well-known New 

 York florist. See Gray, Sillimau's Journal, 3d series, xiii, 1877, p. 138; and some notes 

 by myself, Bulletin Torry Botanical Club, vi, 1879, p. 344. 



t Glover, Agricultural Report, 1855, p. 234, mentions these glands, as well as the inner 

 st-t and their secretion of a " sweet substance, which ants, bees, wasps, and plant-bugs 

 avail themselves of as food." 



{These glands belong, in reality, to an inner whorl of three bracts, alternating with 

 the outer ones, but generally wanting. In stunted plants, especially as cold weather 

 comes on, one or more of these inner bracts may often be found. ((PI. Ill, Fig. 13.) 



