22 



CASSELL'S POPULAR GARDEXIXG. 



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 by gradual 

 decay or by being pushed 

 off by the constantly in- 

 creasing growing point 

 within (Pig. 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, but this latter 

 term is objectionable as 

 conveying an altogether 

 erroneous notion of iden- 

 tity with the chemical 

 substance of which the 



familiar example. The 

 perisperm is filled with 

 starch grains, and other 

 materials suitable for the 

 nutrition of the growing 

 jDoint. This is the sub- 

 stance which constitutes 

 the bulk of the wheat- 

 grain, and which is 

 ground iip to supply our 

 requirements (Fig. 6). 

 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 



Fig. 7.— Seed of Broad Bean after removal of the husk, to 

 show the embryo witnout any perisperm, but with 

 large fleshy seed-leaves or cotyledons, in which food is 

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

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

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

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

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



Fie 



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

 another illustration of the perisperm, filled in this 

 case also with food for the embryo plant. 



The nutritive power of 

 the perisperm is well 

 illustrated by some curi- 

 ous experiments of Yau 

 Tieghem, Avho removed 

 the embryo plant of the 

 Marvel of Peru {Mira- 

 hiliti) from its bed of 

 X^erisperm, 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 gTcw 

 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 

 wdthout the intervention 

 of any perisperm (Fig. 7). 

 In these cases it wall be 

 found that the embryo 

 plant itself is large, and 

 its tissues filled with food- 

 matters. Thus, while the 

 embryo plant or growings 

 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 

 dr}' uj) 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 o-R-n stores have 

 become exhausted. An examination of different 



Tuberous Eoot of Dahlia, serving as food-store. 



