444 



FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



part, either by serving as a mechanism of dispersal, or by fixing the seed in the 

 germinating bed. 



In the case of plants with succulent fleshy fruits, the seeds of which are dis- 

 tributed by birds, it would be extremely disadvantageous for the fruits to b© 

 provided with spines or prickles when ripe. In point of fact, when such structures 

 are present they often disarticulate and fall away as the fruits ripen, so that birds 

 may have unhindered access to them. The fruits of the leguminous Mucuna 



l^ruriens are clad during 

 ^ ' "^^^b©::<>\ their ripening period with 



a felt-work of serrated 

 bristles, which contain an 

 irritating fluid. These 

 bristles cause an intoler- 

 able itching, or even an 

 eruption of the skin, and, 

 so long as they remain on 

 the fruit, effectively guard 

 it from animals. But as 

 the seeds ripen, and the 

 fruit becomes pulpy, these 

 bristles fall away (so it is 

 stated), and animals are 

 no longer repulsed, but 

 devour the pulp, and so 

 disperse the seeds. 



The well-known Hips 

 of Roses which ripen in 

 the autumn, do not fall 

 away from the plant, but 

 remain attached. The 

 seeds are contained in 

 hard and tiny nut -like 

 fruits, which are inclosed in the fleshy and excavated receptacle. They are 

 destined to be distributed by blackbirds, jackdaws, and other birds, which devour 

 the hips for the nutriment contained in the fleshy investment; the little nuts, how- 

 ever, pass out undigested in the droppings in some place more or less distant from 

 the Rose-bush. Whilst these birds, attracted by the coloured fruits, are welcome 

 guests, the case is quite the reverse as regards mice and other little rodents; they 

 gnaw the nuts, and devour their contents, the seeds. But the Rose-hips are well- 

 protected against these animals. The stems and branches, up which they must climb 

 to reach the fruits, are provided with sharp prickles with downwardly-directed 

 points, which give complete immunity against these animals. I have repeatedly, 

 in the late autumn, when the mice desert the fields and take up their winter- 



Fig. 338.— Protection of ripening seeds against animals. 



The Anatto plant (Bixa Orellana) witli flowers and fruit. Three of the fruits have 

 opened sliowing the seeds. (After Baillon. ) 



