THE LIFE -HISTORY OF PLA^^TS. 



89 



with growth, at hoth ends of the arch, confers greater 

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

 the seed, the ladicle, 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 

 embryo 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 

 cases. But it may be 

 well to call attention 

 here to a peculiar ar- 

 rangement first ob- 

 served by M, Flahault 

 in the seedlings of 

 Cucurhitaccce (Melon, 

 Cucumber, &c.). 



In this case, the 

 seed -coats are held 

 down by the aid of a 

 httle 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 dowa, 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 uplifted 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 



rig. 17. —Seedling Bean further advanced, showing the radicle, 

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

 here lengthened and bearing a i>air of leavss. 



hay falling on him. He would first endeavour to get 

 his arched back upright, wriggling at the same time 

 in aU directions to free himself a little from the sur- 

 rounding pressure . , . The man, still wriggling, 

 would then raise his arched back as high as he 

 could, and this may represent the growth and con- 

 tinued gyi-atory mo-^-e- 

 ment of the arching 

 caulicle before it has 

 reached the surface. 

 A.S soon as the man 

 felt himself at all 

 free he would raise 

 the upper part of his 

 body, while still on 

 his knees, and still 

 wriggling ; and this 

 may represent tiie 

 bowing backward of 

 the basal leg of the 

 arch, 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, libei atcf 

 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 

 are either ♦^wo seed-leaves or one. Our great 

 English naturalist, Ray, was the first to make 

 this very important generalisation. Plants \\dth 

 two seed-leaves are technically called Dicoty- 

 ledons or Dicotyledonous ; plants with 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 

 e-lance at a leaf or a flower is in most instances 



