48 



THE GARDENER'S ASSISTANT. 



same mode of growth is observable when the 

 inflorescence is broad rather than long; only, in 

 that case, the outermost flower corresponds to 

 the lowermost in the long inflorescence and 

 opens first, being followed by the others in suc- 

 cession from the margin to the centre. In the 

 definite mode of broad-topped inflorescence, on 

 the other hand, the central flower opens first 

 and the others follow in succession from the 

 centre towards the circumference (fig. 57). 



Subordinate in importance to these main 

 subdivisions of definite and indefinite inflores- 

 cences are various methods of arrangement, of 

 which we can only mention a few : of the indefi- 

 nite forms there is the spike, where the flowers 

 are sessile on a long axis, as in the Arum; the 

 raceme, where each flower is attached to the 

 main axis by a little stalk or pedicel, as in the 

 currant ; the panicle, where branching is carried 

 one degree further, and the little flower-stalk, 

 instead of at once producing a flower, branches, 

 and it is on that branchlet that the flower is 

 formed. Among the broad, flat-topped inflores- 

 cences we have the head or capitulum, where the 

 flowers are "sessile", as in the Sunflower and 

 other Composites; the simple umbel, or truss in 

 garden language, as in the Rhododendron, where 

 they are stalked; the compound umbel, where the 

 stalks branch before bearing flowers, as in the 

 Carrot, and indeed as is characteristic of the 

 "Umbelliferae", to which order the plant named 

 belongs. 



Of definite inflorescences, where the topmost, 

 or the central flower, according to the shape, 

 opens first, the principal variety is the cyme, 

 which may be much branched; but in any case 

 it is the central flower of each little tuft which 

 opens first, or, if it be a long inflorescence, the 

 topmost one. Other variations are described in 

 botanical text-books, to which we must refer for 

 further details. 



One other point may be mentioned, viz. that 

 the leaves on the inflorescence, that is to say 

 those leaves nearest to the flower, are termed 

 bracts. Sometimes they are like ordinary leaves,, 

 at other times they are brightly coloured. Some- 

 times, as in the Arum, one large bract envelops 

 the whole inflorescence. In that case the 

 bract is termed a spathe. In contrast with this 

 is the case where a great number of small bracts 

 are crowded together round a head of flowers, 

 as in the Dahlia or Sunflower. Such a collec- 

 tion of bracts is called an involucre. In the 

 common Globe Artichoke these bracts become 

 succulent at the base, and constitute the edible 

 portion. [m. t. m.] 



CHAPTER VIII. 



REPRODUCTION— THE FLOWER. 



difference between growth and reproduction 

 — Pollen - cells — Egg - cells — Conditions for 

 Flowering — Conformation of the Flower — 

 Parts of the Flower — Fertilization — Hybri- 

 dization — Sports — Division, Separation, and 

 Recombinations of the Nuclear Elements — 

 Seeds, Dispersal of — Germination. 



It is necessary to bear in mind the distinction 

 between growth and reproduction. Growth, as 

 has been pointed out, takes place by extension 

 or subdivision of old cells, and in the more 

 highly developed plants by the formation of 

 buds which are, or may be, the starting-points 

 of shoots and branches. Sometimes also, as we 

 have seen, these buds are separable and grow 

 into plants which, though in a sense independent, 

 are only subdivisions of the original plant. But 

 in the process of reproduction an entirely new 

 individual plant is produced by the co-operation 

 and fusion of two originally separate nuclei or 

 particles of protoplasm — the one male, the other 

 female. The male protoplasm supplies the fer- 

 tilizing substance or sperm, the female element 

 is a detached portion of protoplasm called the 

 egg, which is fertilized by the sperm. As a 

 consequence of this union of two elements an 

 embryo plant is produced. The embryo or seed- 

 ling plant is thus a compound of two parents, 

 and partakes of the characters of both, generally 

 in different, rarely in equal, proportions. The 

 essentials of fertilization are the same in all 

 creatures, but the details differ very consider- 

 ably in different plants. Here we are concerned 

 exclusively with the higher groups, the so-called 

 flowering plants, "Phanerogams", whose male 

 cells, known as microspores or pollen-grains, are 

 formed and contained within microsporanges or 

 outliers, and whose female or egg-cells {mega- 

 spores) are contained within the embryo-sac, itself 

 inclosed within an ovule. 1 



Conditions requisite for the Production 

 of Flowers. 



The production of flowers and of organs of 

 reproduction depends partly on the same con- 

 ditions as those which influence growth in 

 general, but there are some differences to which 

 it is of the greatest importance that the attention 

 of the gardener should be devoted. Very gener- 



i In some Cycads and Conifers fertilization is effected by 

 sperm atozoids as in Ferns, and thus a link is established between 

 the Phanerogams and the so-called higher Cryptogams. 





