22 



CASSELL'S POPXJLAE GAEDENINa. 



But in either case the growing plant is surrounded 

 by a protecting investment in the shape of the husk 

 of the seed, or the scales of the bud (or other device 

 having the same object). 

 With that protecting in- 

 vestment we are not 

 greatly concerned now ; 

 it is not in itself a centre 

 of activity at any time ; 

 and now that we may 

 assume it to have done 

 its work, it is no longer 

 of service, and is dis- 

 carded either hy gxadual 

 decay or by being pushed 

 ofi by the constantly in- 

 creasing growing point 

 within (Fig. 3). 



The Perisperm. — 



Beneath the protecting 

 husk, in the case of the 

 seed, is very frequently to 

 be found a mass of tissue 

 generally of a white 

 colour and floury appear- 

 ance — this is called tech- 

 nically the "perisperm" 

 of the seed (Fig. 4). 

 Sometimes it is called 

 albumen, hut this latter 

 term is objectionable as 

 conveying an altogether 

 erroneous notion of iden- 

 tity with the chemical 

 substance of which the 

 white of eggs furnishes a 

 familiar example. The 

 perisperm is filled with 

 starch grains, and other 

 materials suitable for the 

 nutrition of the growing 

 point. This is the sub- 

 stance which constitutes 

 the bulk of the wheat- 

 grain, and which is 

 ground up to supply our 

 requirements (Kg. 5). 

 Another familiar example 

 is the flesh of the cocoa- 

 nut, which also is filled 

 with food destined for 



the benefit of the young plant, if it be not previously 

 requisitioned for the requirements of mankind. The 

 hard bony stone of the date (Fig. 6) and of some 

 other palms (by no means to be confounded with the 



rig. 7.— Seed of Broad Beat) after removal of the husk, to 

 show the embryo without any perisperm, but with 

 large fleshy aeed-leaves or ootyledons, in which food is 

 stored for the use of the growing plant. In A, the line 

 at c points to one seed-leaf, and ji to the plumule or 

 growing point of the stem. B shows one seed-leaf re- 

 moved ; V is the growing point of the root ; a, the scar 

 formed by the removal of the seed-leaf ; p, the plumule. 



stone of the peach or the shell of a filbert), affords 

 another illustration of the perisperm, filled iii this 

 case also with food for the embryo plant. 



The nutritive power of 

 the perisperm is well 

 illustrated by some curi- 

 ous experiments of Van 

 'Tieghem, who removed 

 the embryo plant of the' 

 Marvel of Peru {Mba- 

 hilis) from its bed of 

 perisperm, and fed it not 

 only with artificial nutri- 

 tive solutions, but also by 

 portions of the perisperm 

 bruised and laid over it. 

 The embryo plant grew 

 almost as well under this 

 system of artificial nurs- 

 ing as under natural con- 

 ditions. 



But such seeds as those 

 of the pea and bean have 

 no perisperm; their em- 

 bryo plant is immediately 

 invested by the seed-husk 

 without the intervention 

 of an}' perisperm (Fig. 7). 

 In these cases it will be 

 found that the embrj-o 

 plant itself is large, and 

 its tissues filled with food- 

 matters. Thus, while tho 

 embryo plant or growing- 

 point of a date-stone is 

 no bigger than a pin's 

 head, that of the pea or 

 bean occupies the whole 

 of the seed ; the plant in 

 this latter case carries its 

 store with it. 



The seed of an orchid 

 is very minute, and is 

 equally destitute of peri- 

 sperm. It is so small 

 that there cannot be much 

 store of nutriment within 

 it ; hence it is clear that 

 it must be enabled to 

 shift for itself from a very 

 early period, or it will 

 dry up and die; while 

 the other seeds we have mentioned are not under 

 the necessity of obtaining supplies from without, un- 

 less it be of water, till after their own stores have 

 become exhausted. An examination of different 



Fig. 8. — Tuberous Boot of Dahlia, serving as food-store. 



