THE I'LOHAL STKM. 743 



or walk from one fascicle ami umbfl to a neighbouring one as if over a flower-strewu 

 surface, thus moving the pollen from place to place and efiecting innumerable cross- 

 ings which would not take place so easily if the flowers were isolated and not 

 collected into inflorescences with a definite order of blossoming. The likelihood of 

 a crossing between did'erent flowera is of coui"se increased with their greater number 

 and consequently plants with grouped inflorescences have so far an advantage over 

 those whose flowers unfold singly at greater distances. Isolated flowers, it is true, 

 possess large, brilliantly-coloured perianth-leaves which serve to allure honey- 

 seeking animals on the wing; but, on the other hand, the same efiect is produced 

 by the accumulation of many small flowers, and au attraction is also afibrded by 

 the development of so-called ray florets on capitula and umbels, as well as by the 

 brightl3'-coloured bracts forming a tuft on the top of cymose and spiked inflores- 

 cences, which is no less effective than the largest corolla. This explains why 90 per 

 cent of plants visited by winged insects bear inflorescences and not isolated flowers. 

 Large isolated flowers only serve the purpose of larger honey-seeking animals, of 

 such butterflies and moths, humming and other honey-seeking birds, which would 

 not be able to obtain the honey from small, conglomerated flowers. But it is a well- 

 ascertained fact that the number of small flies, bees, wasps, and humble-bees which 

 visit flowers greatly exceeds that of larger animals, and this explains why clusters 

 of small flowers occur much more frequently than large single flowers. 



Remarkable correlations with the animal world also exist in other retrions of 

 the plant, but in no other part of the stem do they appear so striking and so mani- 

 fold as in the floral region. Nowhere else can the harmonious co-operation of the 

 members, the practical division of labour, and the mutual aid for the attainment 

 of an end, be seen so plainly and convincingly as in the inflorescence. In many 

 capitula and umbels one portion of the flowers forms the pollen; another develops 

 the ovules ;-a third allures insects; and a fourth prevents the depredations of unwel- 

 come visitors. Most remarkable of all, this practical division of labour within a 

 single inflorescence does not terminate even with the fading of the flowers, but is 

 still continued in the same parts during its subsequent passage into a fruiting state. 

 Many processes give us the impression that the flowei-s collected in a raceme, umbel, 

 or cyme mutually understand one another; thus, for example, in the CmciferiB it 

 often happens that older flowers, whose stigmas have already withered, and wliich 

 have also entirely lost their pollen, allure insects to the adjoining younger flowers, 

 since now, instead of falling, the petals enlarge and adorn themselves with con- 

 spicuous colours, visible at a distance. It also frequently happens that older 

 flowers, whose time is over, vacate the most advantageous position for blossoming 

 in favour of neighbouring younger flowers. When the flower of a nasturtium 

 (Tropccolura) fades, its flower-stalk bends downwards, contracts in a spiral, and 

 hides under the green peltate foliage-leaves, while a new bud pushes into the place 

 where the older flower fonnerly stood; this bud opens next day and awaits insect 

 visits, and hasty observers might think that the same flower had remained there 

 for more than a week. The same thing occurs in Linaria cymhalaria, Ledum 



