40 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



excite the action of the forces to be util- be consumed by the visiting insect, known 

 izecl by the former. It is the possession as Nectars, are produced by certain spe- 

 of both of these classes of provisions cial glands and s 

 which constitutes one of the most impor- 

 tant distinctions between flowering plants 

 and the flowerless, in which latter the 

 male element is almost invariably pro- 

 vided with the power of independent lo- 

 comotion, by which it can reach the fe- 

 male. Provisions for attracting external 

 agents are found chiefly in the form, 

 coloration and size of the flower or of 



stored in or upon con- 

 tiguous receptacles called Nectaries, The 

 presence of these nectaries is commonly 

 responsible for the outgrowth of the ap- 

 pendages to which they are often at- 

 tached (Figs. 52 and 53). At other 

 times a part of the flower not conspicu- 

 ously modified produces and holds the 

 nectar. 



The influences here described are in 



one or more of its parts, the production almost all cases exerted at certain times 



of fragrant and nutritive secretions and 

 the exercise of these influences at the 

 most opportune times. The form of the 

 flower is efficient when it resembles a 



which are especially favorable for secur- 

 ing the desired results. In speaking of 

 the perigone it has been shown that flow- 

 ers vary greatly as to their duration. It 



particular time of day when pollination 

 is most likely to occur. Those which last 



form attractive to an insect the visit of may be further stated that those which 

 which is desirable, or when it is one well perish quickly mature and expand at the 

 calculated to display effectively the color- 

 ation; and it is not impossible that cer- 

 tain forms, like certain colors, are at- for several'days enjoy a daily resting 

 tractive p3r ,se. The forms of nectar- period and another period of greatest ac- 

 bearing plants are, moreover, in most 

 cases, such as to facilitate the collection 

 of the food by the visiting insect, or, when 

 otherwise, to effect special objects to be 

 considered further on. Coloration also 

 may be attractive through its simulation 

 of an insect or merely by its serving to 

 make known to the insect the presence 



tivity, the details of which vary in differ- 

 ent species or classes. Commonly the 

 perigone becomes more or less folded or 

 closed, its form and coloration less con- 

 spicuous, the exhalation of odors entirely 

 suspended or greatly restricted and access 

 to the nectar prevented altogether. At 



the same time that its functions are thus 



or iHKsition of the flower concerned— as a inactive its position is such as to afford 



white, light-colored or lustrous flower, in 

 attracting insects which fly only when 

 there is little light. Flowers are fre- 

 quently modified in size so as to effect 

 these results, and this modification is 

 often secured at the expense of their own 

 sexual functions. Fig. 231 illustrates a 

 cluster of Viburnum flowers, the marginal 

 being light-colored and large, and ad- 

 mirably adapted to attract insects, but 

 destitute of perfect reproduction parts. 

 The odors of flowers similarly, while fre- 

 quently offensive to the human sense, are 

 supposed to be attractive in most cases 

 to the insects whose visits favor their 

 pollination. They are due to the evapora- 

 tion of volatile oils. The glands by which 

 these are excreted and in which they are 

 stored may be distributed through the 



it protection of various kinds from dan- 

 gers which are especially imminent during 

 the hours in which it rests. This condi- 

 tion of inactivity or rest is commonly 

 spoken of as the sleep of the flower, it 

 occurs at such a period of the day as finds 

 the agencies specially adapted to pollina- 

 tion in its case themselves enjoying their 

 rest. As these again become active, the 

 flower "awakens" and all the conditions 

 above noted are reversed, or at least such, 

 of them as affect the flower in question. 

 Flowers in which this active period oc- 

 curs during the day, whether they endure 

 for but one day or longer are called Diur- 

 nal; those in which it occurs at night are 

 called Nocturnal. Besides the regular 

 daily resting period, a great many flowers, 

 by virtue of special sensitiveness, possess 



tissues of all or certain of the floral parts, the power of assuming such a condition 



or their presence may be restricted to the 

 special appendages described below. The 

 nutritive substances other than pollen to 



on special occasions when the conditions 

 call for it. 



Humming-birds, as well as insects, are 



