THE LIFE-HISTOEY OF PLANTS. 



89 



■■with growth, at both ends of the arch, confers greater 

 power in, as it were, upheaving the plumule. In 

 the seed, the radicle, tigellum, and seed-leaves are 



■ often so placed as to be in one straight line ; but 

 when such seeds begin to germinate, the arched 

 appearance of the caulicle is as marked as it is in 

 those cases where the 



embrj'o plant is natu- 

 rally coiled up in the 

 seed. 



The necessity for a 

 fulcrum or bearing of 

 some kind has been 



■ alluded to, and the way 

 in which that necessity 

 is met in ordinary 

 eases. But it may be 

 well to caU attention 



. here to a peculiar ar- 

 i-angement first ob- 

 served by M. Flahault 

 in the seedlings of 

 Cucurbitaceie (Melon, 

 "■ Cucumber, &c.). 



In this case, the 

 .-seed -coats are held 

 down by the aid of a 

 little hook or peg, 

 which protrudes from 

 the upper part of the 

 radicle or lower por- 

 tion of the caulicle, and 

 becomes hitched over 

 the lower part of the 

 split seed-coat, fasten- 

 ing it down, as it were, 

 and thus giving 

 greater grip to the 

 descending radicle and 

 ■ to the arching caulicle. 

 In accidental cases 

 where this peg is not 

 developed, or is by 

 some means prevented 

 from effecting its pur- 

 pose, then the cotyledons are upHfted with the seed- 

 coats still attached to them. 



It is very probable that other arrangements of 

 this nature exist in plants, but they have as yet 

 hardly been looked for, though obviously the matter 

 is one of some practical importance. We may con- 

 clude this portion of our subject by giving the 

 substance of Darwin's illustration of the way in 

 which the seedling plant breaks through the earth. 

 Let us suppose a man to be thrown on his hands and 

 knees, and at the same time to one side, by a load of 



Fig. 17.— Seedling Besui further advanced, showing the radicle, 

 the caulicle, the cotyledons, and above them the plumule, 

 here lengthened and hearing a pair of leaves. 



hay falling on him. He would first endeavour to get 

 his arched back upright, wriggling at the same time 

 in all directions to free himseU a little from the sur- 

 rounding pressure . . The man, stiU wriggling, 

 would then raise his arched back as high as he 

 could, and this may represent the growth and con- 

 tinued gyratory move- 

 ment of the arching 

 caulicle before it has 

 reached the surface. 

 As soon as the man 

 felt himseU at all 

 free he would raise 

 the upper part of his 

 body, while stUl on 

 his knees, and still 

 wriggling ; and this 

 may represent the 

 bowiog backward of 

 the basal leg of the 

 aioh, which in most 

 cases aids in the 

 withdrawal of the 

 seed-leaves from the 

 buried and ruptured 

 seed - coats, and the 

 subsequent straighten- 

 ing of the. whole 

 caulicle, the wriggling 

 movement still con- 

 tinuing. 



The Seed-leaves, 



— The lengthening of 

 the caulicle, as just 

 alluded to, liberate? 

 the seed - leaves or 

 cotyledons, concern- 

 ing which organs we 

 must say a few words. 

 In the seedlings of 

 all flowering plants, 

 disregarding a few 

 exceptions insignifi- 

 cant in number, there 

 seed-leaves or one. Our great 



are either two 

 English naturalist. Hay, was the first to make 

 this very important generalisation. Plants with 

 two seed-leaves are teohnically called Dicoty- 

 ledons or Dicotyledonous ; plants vpith a single 

 seed-leaf are called Monocotyledons or Monoco- 

 tyledonous. This was a very important generali- 

 sation to make, because it is associated with other 

 characteristics of leaf, stem, and flower, of external 

 appearance and internal structure ; so that a mere 

 glance at a leaf or a flower is in most instances 



