446 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



branches keep browsing uniiuals away, whilst those inserted lower down, which are 

 directed earthwards, prevent mice from climbing up the plant. 



A peculiar protective contrivance has been observed on the calyx of several 

 Labiates, e.g. Thymus, Calamintha, Ballota. The corolla falls away after fertiliza- 

 tion, but the calyx persists, forming a sheathing envelope for the 4 nutlets. For the 

 better protection of these nutlets the mouth of this cup-like envelope is closed by 

 the development of a crown of hairs, which is impenetrable to small, seed-devouring 

 animals. A further use of these envelopes in seed-dispersal will be alluded to in 

 another place. 



In other cases fruits are protected against unwelcome guests, not by spiny 

 structures, but by the elongation of their stalks during ripening, rendering them 

 inaccessible. Thus it would be a difficult feat for a mouse to reach the pendent 

 pods of the Pea (Pisum), or those of the Vetches (Vicia diometorum, V. pisiformis, 

 V. sylvatica). Should by any chance a pod be accessible to these animals, by some 

 other route, it is as good as lost, as the nutritious seeds of these plants are much 

 sought after by them. Cherries also, on their long stalks, no doubt derive consider- 

 able immunity from earwigs, centipedes, &c., as those which fall to the ground 

 are speedily attacked and devoured. 



In the case of seeds whose dispersal depends on the attraction of animals by 

 sweet, fleshy pericarps, these tissues are the reverse of appetizing before they are 

 ripe; not until the seeds are ready to be separated from the parent plant do fruits 

 of this kind become attractive. It is only necessary to cite as instances unripe 

 Cherries, Plums, Apples, and Grapes. It was stated on a previous occasion (vol. i. 

 p. 462), when dealing with chemical changes occurring in plant-tissues, that the 

 fleshy parts of fruits are rendered disagreeable to animals before they are ripe by 

 the presence of bitter or poisonous glucosides, &c. Later on these substances are 

 altered, perhaps under the influence of the acids, which are present in large quanti- 

 ties in unripe fruits, and their place taken by sugars and other harmless materials; 

 thus, what is at first unattractive, and even repulsive, becomes, on ripening, a 

 nutritious food, much sought after by animals, which, at the same time, uncon- 

 sciously disperse the contained seeds. In this connection the Walnut (Juglans 

 regia) is very instructive. Until the seed contained in the "nut" (here really the 

 stone of a drupaceous fruit) is ripe, the latter is surrounded by a fleshy investment 

 rich in tannin. It is not known at this stage that the "nuts" are ever interfered 

 with by nut-crackers or other animals. But on the ripening of the seed the fleshy 

 envelope splits, and the "nut" becomes accessible. 



In other cases it is not by acids or bitter stuffs that the seeds are protected, but 

 by strong-scented resinous or sticky substances, which are contained in the cells 

 and passages of the fruit. Thus, in the scales of the cone of the Arolla Pine {Pinus 

 Oembra) quantities of resin are present until the seeds are ripe. If the cones be 

 cut with a knife this resin escapes, and can only be removed from the blade with 

 the utmost difficulty. Were a nut-cracker to peck the scales at this stage to 

 obtain the young seeds, its beak would get all besmirched with the resin. It 



