The President's Address. By Lord Avebtiry. 291 



birds. In Bidens the achenes terminate in barbed bristles. In the 

 Burdocks {Arctium) the bracts surrounding the flower-head are 

 strongly hooked at the apex, and evidently arranged so that the 

 whole head should be carried away by some passing animal. 



In a large proportion of the species the achenes are distributed 

 by the wind in consequence of the presence of a pappus. In some 

 cases it is but slightly developed. In Arctium it has possibly 

 degraded, being replaced by the hooked barbs. 



Other genera possibly represent cases in which it is even now 

 being evolved. In Centaurea, for instance, it is short, and cannot 

 be very efficient. 



In many genera, however, it is highly and beautifully developed. 

 The hairs of the pappus are in some species simple, and in others, 

 which seem to represent the highest development, plumose. 



The life-history of the plant seems often arranged with refer- 

 ence to them. In the common Dandelion the bud lies prostrate on 

 the ground ; when the florets are ready to open, the flower-stalk 

 raises itself so as to get all the sun, and be as conspicuous as 

 possible to insects. Every evening and in wet weather it closes, so 

 as to preserve its precious charge from too much wet. I once kept 

 one awake, however, all night by keeping it in the light of an 

 Argand lamp. When the flower is fertilised, the stalk once more 

 becomes horizontal, or nearly so, thus endeavouring to avoid the 

 dangers which might befall it if it remained upright while the seeds 

 were maturing. This takes about a fortnight, and when the seeds 

 are ripe the flower-stalk again rises perpendicularly, thus assum- 

 ing the position most favourable to assist in the dispersal of the 

 achenes by the wind. Where the grass is short, as for instance on 

 lawns, the intelligent plant keeps its flower-stalk also short ! 



In the Dandelion {Taraxacum), the Lettuce {Lactuca), and 

 some others, the achenes terminate in a long beak. The object of 

 this, perhaps, may be to carry the upper end further from the 

 disk of the flower-head, and thus give more space for the expansion 

 of the pappus. 



In the species hitherto mentioned, the seeds are all alike. 



In Leontodon hirtus, however, most of the fruits have a well- 

 developed pappus ; but those of the outer row have none. 



In Hypochceris glabra the pappus of the outer florets is sessile, 

 while the inner ones are on a long beak. 



The common Calendula. (Marigold) (fig. 80) of our gardens is 

 an even more interesting case. Three devices for dispersal are 

 united in each head. The outer achenes (fig. 81) are narrow, and 

 bent into a curve forming three parts of a circle, and well adapted 

 to hang on to the fur of any passing animal. Then follow a 

 certain number which are puffed out with wide wings (fig. 82), and 

 are evidently intended for dispersal by wind. Towards the centre 

 the achenes are smaller, and much resemble small green or brown 



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