SEED 



logical condition* are not understood and in dis- 

 poied within tin- seed in three different wn\s in 

 relation i<> the embryo. It may lie in the cells of 

 the nucellus, iiniiind but not within the embryo-sac, 



A B 



J m 



Diagram showing gen rl structure of Seed ( from Parker's 

 iit-i 



A, lection of orulr : b, pollen-tube; r. nucellus; /, accessory 

 ecus or lynerghln- : g, ovum "r i>xx-cell ; , central nucleus of 

 embryo-ac ; i. antipodal cells of embryo-mc; k, embryo-sac. 



B, embr) O-MIC. bowing o. lunprniior ; b, embryo or segmented 

 ovum ; c. nuclei ; d, nonole*. 



C, section of a seed, ibowing o. the micropyle ; b, embryo with 

 embryonic root ; r embryonic item ; d, cotyledons ; t, external 

 ned-coat ; /, eaduripenii ; g, perlaperm. 



as in the Heeds of bananas and ginger ; then we 

 call it pei i-pcrm. Or it may lie in more intimate 

 relation to the embryo, within the embryo-sac 

 ( where a median nucleus seems to bear some rela- 

 tion to ite formation), as in the seeds of wheat 

 and castor-oil ; then we call it endosperm. Some- 

 times there may be lioth cndos|>erni and |>erispeim. 

 as in water-lilies. But in many cases there is 

 neither endosperm nor |w'ripeint, all the food 

 material being stored within the embryo itself 

 in its cotyledons as in the pea and wallflower, 

 apple and almond. Such seeds are somewhat con- 

 fusedly called ex-albuminous. 



The food materials, which are so often and by no 

 means accurately summed up in the term albumen, 

 vary in different kind* of seeds. Imt in a general 

 way we may say that they consist of starchy, 

 fatty, and nroteid substances in varying propor- 

 tions. In the development of animal* they have 

 their analogue in the yolk, and the analogy is 

 especially true of the endosperm which in formed 

 within the embryo-sac. But this analogy cannot 

 be pressed, anil it is perha|>s more important to 

 notice that the three ways in which the nntrimriii 

 occurs in the nucellus ( |x!risperm ), in the embryo 

 sac (fii.|i|MTin ), and in the embryo iteelf form an 

 intelligible series. The perispenn, which is least 

 fonimiin, occurs in the nucellus an outgrowth of 

 the carpel i.e. in the s|>rangium of tin- sporophyte 

 generation (see FI.OWKK, FKKN, Ovri.K). The 

 endo-pcini occurs in the embryo HOC, has it-- ccnttc 

 in a central nucleus (formed from the fusion of two 

 of tin- eight inn-lei into which the primary Hporc. 

 cell divides), and is therefore included in the pio 

 tliHlliuin of the gamoiihyle generation. Lastly, 

 and most frequently, (lie nutrition mav In 1 stored 

 within the embryo winch result* from tne fertilisa- 

 tion of the egg-cell of the gamophyte. 



.^/, iirture <if tin ,'ln-ril in n/ntinii In tlir 



I',:i.:i 4 i,n ../ //.. l-'.niliri/ii. A the embryo plant is 

 delicate Blriictnre, and as its separation from the 

 parent plant is attended with vicissitudes, for the 

 Med may be blown or carried into unfavourable 

 conditions, and as most of the seeds which are 

 liberated are not at once ready to germinate, it ia 



ini|M>rtant that the life of the embryo should be 

 piotectcd. This necessary protection is supplied 

 in various ways. Around the ovule a double invest- 

 ment usually grows, and part of this investment is 

 modified a> the husk of the seed. The modification 

 becomes marked as the seed grows i ipe. as it begins 

 to be ready for separation from the patent, as ito 

 supply of water uegins to fail, as its vitality 

 becomes more dormant ; in fact the modification, 

 which is a most useful one. is in part a necessary 

 result of the physiological conditions of seed-ripen- 

 ing. In the modified husk it is generally possible 

 to distinguish a thin, relatively unimportant inter- 

 nal legmen from an outer, thicker, resistent testa. 

 This testa may be leathery or woody, fleshy or 

 gelatinous, smooth or hairy ; it is variously adapted 

 for the protection of the enclosed embryo. \Ve 

 may compare it to the shell or case which often 

 surrounds the animal embryo. There is usually 

 some relation between the nature of the seed -coat 

 ami that of the pericarp which surrounds the whole 

 fruit ; for in indehiscent fruits with tough walls (as 



in aclienes and nuts) the s l-coat remains thin. 



while in dehiscent fruits the seed-coat is usually 

 thick and hard. See GwxiKAI'IIlCAL. Dl.sTHIBU- 

 TION. 



Apart from the husk, the ripe seed is some- 

 times marked liy a growth from it.s base or stalk. 

 This is called the aril, and may lie hairy as in 

 willows and poplars, fleshy as in Euonymus, pecu- 

 liarly shredded as in the mace of Mijrixtira aro- 

 nuittca or nutmeg. When the growth from the 

 base or from the funiciilus of the seed is all on one 

 side, it is called a caruncle, as in Ckelidottium 

 innjiix, \'ii>lit trini/ur, and liiciniis coiniiniiiis. The 

 outer surface of a liberated seed may also bear 

 a mark at the place (hilunt) where it separated 

 from the funiciilus ; this is well seen in the 

 common bean. Sometimes also a. small opening or 

 depression (rirntririilii) persists as a remnant of 

 the micropyle or aperture by which the pollen-tube 

 passed between the coats of the ovule. In many 

 cases the region marked by an external scar, corre- 

 sponding to hiliim or to mieropyle or to both, is 

 of special importance, the tissue of the seed-coat 

 being modified so as to act as a sponge through 

 which water soaks in to the embryo within. Many 

 of the hard coats of seeds have, instead of this 

 special sponge, numerous minute canals perforating 

 their dense substance. 



Structure of the Seed considered in relation to 

 Seed-scattering. Already in the article Fisrir 

 reference bos been made to adaptations which 

 secure the dispersion of the seeds. Oftenest the 

 dispersion depends upon the fruit, which may burst 

 violently so that the seeds are scattered, or may lie 

 juicy and palatable so that it is eaten by birds and 

 other animals, the' indigestible seeds being in this 

 wav carried far and wide. Sometimes the fruit 

 anil the seed are virtually though not technically 

 the same, as is the case in thistle-down, in which 

 each little winged fruit Itome aliout by the wind 

 contains a single seed. Sometimes, however, the 

 seeds themselves are borne about by the wind, as in 

 willows and (Kiplars, willow-herbs ( Kpilobiiim ), cin- 

 chona, Asr/' /!"' .\'/, tiii'it. \<\ The hairs which serve 

 ox parachutes to the seeds of poplars, willows, and 

 the like are accessory growths outside the seed; 

 a similar rich growth of cottony bait is character- 

 istic of (lossy piiim and Kriodendron. It should 

 also lie noted that in many coses the seed is 

 adapted to anchor itself, for the surface is often 

 ridged or peaked, as in Hyoscyamiis, Papaver, 

 Nigel la, or liecomes glutinous in moist places, as in 

 flax and some species of I'lantago. 



For further details M to the structure of teeda, consult 

 morphological works inch u Nachs'i Text-book of Rolii n // ; 

 for further detail* w to seed-scattering and the like, * 



