HYBRIDS 



genera. There are technical terms to designate the 

 various kinds and degrees of crossing. 



It was formerly held that inability to make fertile Hy- 

 brids is proof that the forms are distinct species; and 

 contrariwise, that plants which make fertile crosses are 

 of one species. Hybridization has also been made a test 

 of genera. These notions are now given up, for cross- 

 ing and classification belong to two unlike categories of 

 facts. Species and genera are not entities in them- 

 selves, but are mere artificial groups made by men for 

 their convenience when writing and speaking of living 

 things. Crossing is a biological phenomenon. 



Hybrids are unusual facts in nature ; that is, they 

 are rare compared with the whole number of plants. 

 On the other hand, cross-breeds are usual. Most flow- 

 ers are so constructed as to favor cross-pollination. 

 Cross-breeding is one of the prime means of inducing 

 slight variations and of invigorating a type. Upon the 

 variations which arise from crossing and other means, 

 natural selection operates in the production of new 

 forms. But it is significant that these new fonns usu- 

 ally come about slowly and gradually. It is the desire 

 of the cultiv:itor to produce new forms quickly and of 

 pronounced distinctness. He therefore employs cross- 

 ing between unlike types, or species, hoping thereby to 

 secure wider departures. In nature, the cross-breed is 

 the beginning of a process of breeding: it starts off the 

 variation. Man is often tempted to look upon the Hy- 

 brid as the end. If the products of a given cross are 

 not to his liking, he throws them away and tries again. 

 The most expert plant-breeders, however, now hybridize 

 to get a"break," and thenceforth depend chiefly on selec- 

 tion to realize their clear-cut ideals, particularly in seed- 

 propagated plants. 



To man Hybrids are of no value unless they can be 

 propagated. By seeds they usually vary immensely: it 

 is difficult to "fix" them so that they will come true. 

 By cuttings or layers or division, however, the character 

 of the parent may be propagated with practical cer- 

 tainty: the original plant is divided, and the parts are 

 put on the market. Nearly all commercial Hybrids are 

 of plants which are thus propagated by asexual parts : 

 Kieffer pear. Hybrid grapes, Wilson blackberry. Wild 

 Goose plum, cannas, roses, begonias, anthuriums, fuch- 

 sias, pelargoniums, rhododendrons. Since the Hybrid 

 is variable when propagated by seeds, continued selec- 

 tion, or plant-breeding, must be employed to fix and es- 

 tablish a desirable type. 



It is thus seen that hybridization rarely gives rise to 

 dominant horticultural seed-races, but rather to an in- 

 dividual plant which may be disseminated by some di- 

 visional means of propagation. The seeds of Hybrids — 

 as of the modem cannas — may give rise to good varie- 

 ties, and they may not; but these new varieties are, in 

 their turn, usually propagated bymeans of asexual parts 

 if they are to be kept true. 



Practically there is no certainty in hybridization. 

 Rarely can a man picture to himself an ideal variety, 

 and then by means of hybridization produce it. He 

 hybridizes plants which possess some of the character- 

 istics of the desired or ideal variety, and then takes his 

 chances. True plant-breeding sets an ideal, and then 

 reaches it by working along certain deiinite lines. It 

 seeks first to secure a variation in the desired direction: 

 this may be secured by means of crossing, change of 

 soil, modification of food supply, and other changed con- 

 ditions. It seeks, then, to preserve or augment the form 

 by means of definite selection. 



We are not yet able to formulate positive laws of hy- 

 bridization. Every Hybrid is a law unto itself. By 

 the study of many examples of hybridization, one is able 

 to construct an average of probabilities as to what will 

 or what will not occur in a given case: but the given 

 case may contradict all the probabilities without ap- 

 parent cause. Hybridization is an empirical subject. 



One can not tell what species will or will not hybridize 

 except })y trying. Hundreds of species have been tried, 

 and for them the knowledge is more or less exact. 

 Plants hybridize most freely which are the subjects of 

 much care and coddling: the orchids are the best ex- 

 amples. In these groups. Hybrids are chiefly fanciers' 

 plants, valuable often only because they are Hybrids or 

 are rare and curious. One cannot tell beforehand 



50 



HYDRANGEA 



783 



whether the products of any hybridization will be exact 

 intermediates, or in what way or degree they will carry 

 over or blend the parental characters. As a rule, the 

 more closely akin the species, the more perfect will be 

 the blending or amalgamation of the two. See Pollina- 

 tion. 



The literature of hybridization is extensive but scat- 

 tered. The standard text is i^ocke's'iDie Pflanzen-Misch- 

 linge," 1881. The possibilities of hybridization as a factor 

 in plant-breeding are presented in many aspects in 

 the "Hybrid Conference Report " of the Royal Horticul- 

 tural Society, London, 1900. There are special books de- 

 voted to orchid Hybrids (see Orchids). In North America 

 there has been little fundamental writing on the subject. 

 See an excellent paper by Swingle and Webber, Year- 

 Book of theU. S. Dept. Agric. 1897; papers in Amei-i- 

 can Gardening, 1899, pp. 397, 413, 431 ; Bailey's "Plant- 

 Breeding," 1895. L. H. B. 



HYDRANGEA (Greek, hydor, water, and aggeion, 

 vessel ; alluding to the cup-shaped fruit). Saxifragd- 

 ceie. Very ornamental deciduous shrubs, with oppo- 

 site, simple, rarely lobed, petioled Ivs. and small, white, 

 bluish or pinkish fls. in corymbs or panicles, bearing 

 usually marginal .sterile fls., with enlarged showy se- 

 pals, or in some varieties all the fls. are sterile and en- 

 larged : fr. a small, insignificant capsule. U.panicu- 

 lata is the hardiest of all, but H. arbore.'<ce)i.<<, II. riidiata 

 and H. Bretschneideri are also ;iliiin,st lianly North, 

 while M. quercifolia and petii'laris nipiirr ;it least a 

 very sheltered position and II. Ifr/cusis, n iKiiita, in- 

 volucrata and virens are still mure teuder, and can hardly 

 be grown outdoors North except when well protected and 

 sheltered. They grow best in a rich, porous and some- 

 what moist soil and thrive well in partly shaded posi- 

 tions, but flower more freely in full sun if they only have 

 sufficient moisture. All Hydrangeas are well adapted 

 for borders of shrubberies, and H. paiiiculafa and hor- 

 tensis, especially the varieties with sterile fls., are very 

 showy as single specimens on the lawn. In warmer cli- 

 mates the latter is sometimes used for ornamental 

 hedges (see G.C. III. 24:337 and 456); but it is not 

 hardy in the North. These and also most of the 

 other species should be pruned in fall or early spring, 

 and the branches of the previous year cut back to 1-3 

 pairs of buds, according to the growth of the branches 

 and the desired size of the panicles; if only slightly 

 pruned the panicles will be many but small. Sometimes 

 they are cut back every year almost to the ground and 

 produce then enormous panicles, which, however, usu- 

 ally need artificial support and lack the gracefulness of 

 less severely pruned plants. B. paniculata, var. gran- 

 di flora can "be grown in a small standard tree; for this 

 purpose vigorous young plants should be selected and 

 planted in rich soil, and cut down to the base. The 

 strongest shoot of each plant will attain by fall the 

 height of 4-6 ft., if freely manured and watered during 

 the summer; in autumn, all the weaker branches are 

 cut ofl', and in colder climates the plants should be 

 lifted and stored in a frost-proof pit or cellar, since the 

 wood is not usually sufficiently ripened to withstand 

 severe frost. In the following year the top of the stem 

 is .allowpil to branch. The weaker basal shoots may be 

 piij^'iMl down to make new plants. Strong-growing varie- 

 ties i.f /[. lim-lensis may be treated in the same way if 

 stiinilard plants are desired. 



//. hoiietisis, which cannot withstand much more 

 than 10° of frost, is in the North much grown as a pot- 

 plant, especially the more showy varieties with large 

 heads of sterile fls., and is extensively used for outdoor 

 decoration during the summer. Late in fall, when the 

 Ivs. have fallen after frost, the plants are moved to a 

 frost-proof cellar and kept rather dry until spring, when 

 they are repotted in new soil and the growth of last 

 year cut back to 1 or 2 pairs of buds. As a suitable soil 

 may be recommended a mixture of loam, leaf -mold and 

 sand, with ground bone, dried cow manure or some other 

 kind of manure added. During the summer a liberal 

 supply of water should be given, also occasionally ap- 

 plications of liquid manure, until the fls. have developed. 

 They may also be planted in the open ground during 

 the summer, lifted late in fall with a large ball of earth, 

 stored over winter in a coldframe or pit and planted out 



