422 



NA TURE 



\Scpt. 24, 1874 



T^ 



COMMON WILD FLOWERS CONSIDERED IN 

 RELATION TO INSECTS* 

 11. 

 'HE Common Heaths (Erica tetralix and E. dnerea) offer us 

 another very ingenious arrangement. In E. tetralix (the 

 Cross-leaved Heath), for instance, the flower is in the form of a 

 bell (Fig. 15), which hangs with its mouth downwards, and is 

 almost closed by the pistil (st), which represents the clapper. 

 The stamens are eight in number, and each terminates in two 

 cells, which diverge slightly, and have at their lower end an 

 oval opening. But though this opening is at the lower end of 

 the anther cells the pollen cannot fall out, because each cell, 

 just where the opening is situated, touches the next anther cell, 

 and the series of anthers thus form a circle surrounding the pistil 

 and not far from the centre of the bell. Each anther cell 

 also sends out a long process, which thus forms a series of 

 spokes, standing out from the circle of anthers. Under these 

 circumstances, a bee endeavouring to suck the honey from the 

 nectary cannot fail firstly to bring its head in contact with 

 the viscid stigma, and thus to deposit upon it any pollen 

 derived from a previous visit ; and secondly, in thrusting its 

 proboscis up the bell, it inevitably comes in contact with one of 

 the anther processes, which acts like a lever and dislocates the 

 whole cha'n of anther cells when a shower of pollen lalls from 

 the open anther cells on to the head of the bee. t 



In the allied genus Vaccinium there is a similar arrangement, 

 but the anther cells are closed, not by touching one another, but 

 by resting against the style, so that the style itself closes the 

 openings until the anthers are distributed by the proboscis of the 

 bee. V. uli^inosum is mucli larger than V. myrtillus, and con- 

 sequently more conspicuous ; V, viyrtillus, on the other hand, 

 has the compensating advantage of being richer in honey. 



The genus Arbutus also is said to agree in essentials with 

 Vaccinium. 



In many cases the effect of the colouring and scent is greatly 

 enhanced by the association of several (lowers on one branch or 

 raceme, as, for instance, in the Wild Hyacinth, the l,ilac, and 

 othc rfamiliar instances. In the great family of Umbellilerie this 

 arrangement is still further taken advantage of, as in the common 

 Wild Chervil {Cherophylluni sy/falrc). 



In this group the honey is not, as in the flowers just described, 

 situated at the bottom of a tube, but lies exposed, and is there- 

 fore accessible to a great variety of small insects. The union of 

 the florets into a head is, moreover, not only of advantage in 

 rendering them more conspicuous, hvX also effects a considerable 

 saving of time, as it enables the insects to visit a given number 

 of insects more rapidly, and consequently renders their fertilisa- 

 tion raore certain than if they had stood singly. 



The self-fertilisation which, in small flowers such as these, 



* Continued from p. 4of>. 



\ Popular Science Jicl'iew, April 1870. 



would otherwise naturally occur, is provided against by the fact 

 that the flowers are generally proterandrous, that is to say, the 

 stamens ripen before the pistil, and the latter is not mature until 

 the former have shed their pollen. In some cases, as, for instance, 

 in Myrrhis, the flowers of one head are all firstly in the male 

 condition, and subsequently in that with mature stigmas, none of 

 them arriving at the second stage until they have all passed 

 through the first. 



In CJierciphylliint the petals are not symmetrical, the outer 

 ones being considerably larger than the others, and in many 

 umbellifers the llorets themselves on the outer edge of the bunch 

 or umbel are considerably larger than the inner ones. 



This distinction is carried still further in the Composite, where 



also the florets are so closely packed together that the whole 

 umbel is commonly, though of course incorrectly, spoken of as 

 a flower. 



For instance, the heads of the common Daisy, as I need 

 hardly mention, are not strictly speaking flowers, but bunches of 

 flowers closely packed together on a common base or receptacle. 



The advantages of this arrangement are : — 



1. That the flowers become much more conspicuous than 

 would be the case if they were arranged singly. 



2. That the facility with wliich the honey is obtained renders 

 them more attractive to insects. 



3. Thit the visits of the insects are more likely to be effectual, 



Fic. 19. Fig. 20. 



since the chances are that an insect which once alights, touches 

 several, if not many, florels. 



No wonder, therefore, that the Composita; are the most exten- 

 sive family among flowering plants, are rej^resented in every 

 quarter of the globe and in every description of station,* and 

 contain nearly leu thousand species. 



If we take, for example, the common Feverfew, or large 

 white Daisy (C/n ysaiit/u-nniin partliLiiiiim], which has been 

 well described by Dr. Ogle,t the flower-heads consist of an 

 outer row of female florets, in which the tubular corolla ter- 

 minates on the outer side in a white leaf or ray, which doubtless 



» Eenlham, "Handbook of the British Flo 

 >oc. 1873, p. 33S. 

 t Popular Science Kez'tntf, Apnl 1870. 



vol 1. p. 403 ; Jour. T.i 



