1^8 THE POPULAR SCIENCE MONTHLY. 



In the first place, then, during growth, seeds in many cases require 

 protection. This is especially the case with those of an albuminous 

 character. It is curious that so many of those which are luscious when 

 ripe, as the peach, strawberry, cherry, apple, etc., are stringy and al- 

 most inedible till ripe. Moreover, in these cases, the fleshy portion is 

 not the seed itself, but only the envelope, so that even if the sweet 

 part is eaten the seed itself remains uninjured. 



On the other hand, such seeds as the hazel, beech, Spanish chestnut, 

 and innumerable others, are protected by a thick, impervious shell, 

 which is especially developed in many Proteacece, the Brazil-nut, the 

 so-called monkey-pot, the cocoanut, and other palms. 



In other cases the envelopes protect the seeds, not only by their 

 thickness and toughness, but also by their bitter taste, as, for instance, 

 in the walnut. The genus Mucicna, one of the Legumiiiosce, is re- 

 markable in having the pods covered with stinging hairs. 



In many cases the calyx, which is closed when the flower is in bud, 

 opens when the flower expands, and then after the petals have fallen 

 closes again until the seeds are ripe, when it opens for the second time. 

 This is, for instance, the case with the common herb-robert ( Gerani- 

 um Mohertiamiin). In Atractylis cancellata, a South European plant, 

 allied to the thistles, the outer envelopes form an exquisite little cage. 

 Another case, perhaps, is that of Nigella, the " Devil-in-a-bu&h," or, as 

 it is sometimes more prettily called, " Love-in-a-mist," of old English 

 gardens. 



Again, the protection of the seed is in many cases attained by curi- 

 ous movements of the plant itself. In fact, plants move much more 

 than is generally supposed. So far from being motionless, they may 

 almost be said to be in perpetual movement, though the changes of 

 position are generally so slow that they do not attract attention. This 

 is not, however, always the case. We are all familiar with the sensi- 

 tive-plant, which droops its leaves when touched. Another species 

 (Averrhoa hilbnhi) has leaves like those of an acacia, and all day the 

 leaflets go slowly up and down. Desmodium gyrans, a sort of pea 

 living in India, has trifoliate leaves, the lateral leaflets being small and 

 narrow ; and these leaflets, as was first observed by Lady Monson, are 

 perpetually moving round and round, whence the specific name gyrans. 

 In these two cases the object of the movement is quite unknown to us. 

 In Dionoea, on the other hand, the leaves form a regular fly-trap. 

 Directly an insect alights on them they shut up with a snap. 



In a great many cases leaves are said to sleep ; that is to say, at 

 the approach of night they change their position, and sometimes fold 

 themselves up, thus presenting a smaller surface for radiation, and being 

 in consequence less exposed to cold. Mr. Darwin has proved experi- 

 mentally that leaves which were prevented from moving suffered more 

 from cold than those which were allowed to assume their natural posi- 

 tion. He has observed with reference to one plant, Maranta arundi- 



