;22 



NATURE 



[January 7, 1915 



by the Scots pine. Plots of its seedlings, raised from 

 seed of trees in the forests of Scotland, Russia, Swit- 

 zerland, etc., differ in vigour and in other respects 

 (immunity to certain fungi, etc.), when all are grown 

 together under identical conditions. Such varieties, 

 with slight differences of structure, may be called 

 races, and are of great practical importance in 

 forestry. Only seeds of the best race, that is, from 

 vigorous trees of the most suitable locality, should be 

 used. 



A sport is usually a solitary phenomenon, arising 

 either as a sporadic peculiar seedling from a seed, 

 or developing out of a bud on a tree as a single 

 branch with some peculiarity of twig or leaf. A sport 

 may be looked upon as a freak, not forming the 

 starting point of a new species, but speedily becoming 

 extinct if left to nature. Sports, when of interest on 

 account of the curiosity or the beauty of their appear- 

 ance, are propagated usually by grafts, cuttings, or 

 layers ; being only in rare cases perpetuated by seed. 

 Some sports are due to arrested development. The 

 tree, in the course of its life, often passes through 

 stages, like those of an insect. The seedling of many 

 species differs from the adult tree as a larva from a 

 butterfly. The infant ash has simple leaves. The 



Fig. I. — Adult foliage of common ash on left, of simple-leaf ash on right ; 

 two ash seedlings in the middle, showing i^rimary leaves above the pair 

 of cotyledons. 



sport known as the simple-leaf ash is simply a seed- 

 ling ash, which has never progressed to maturity and 

 may be called a persistent larval form (Fig. i). 



Abnormal colouring of leaves, so-called variegation, 

 is a sport, usually starting as a solitary branch on an 

 otherwise normal tree, which, when noticed, is pro- 

 pagated by grafting. Deeply-lobed, crumpled, pitcher- 

 like, and other abnormal leaves occur in many species, 

 and are propagated as curiosities. In sports, reversion 

 is often seen ; thus on a fern-leaf beech one or two 

 branches w-ith normal leaves are not uncommon. This 

 reversion may be due to the influence of the stock, 

 as these sports are usually grafted ; or it may be 

 explained as the triumph locally of normal over 

 abnormal factors. Such reversions are never seen in 

 hybrid trees. The occurrence of a sport seems to 

 predispose to further sporting ; a tree with leaves 

 abnormal in shape will sometimes take on, in one 

 branch, abnormal colour as well. These double sports 

 are common in the holiy. 



Hybrids are combinations of two species or of two 

 varieties, which arise either in the wild state or in 

 cultivation. They are met with in nature as rare 

 individuals on the boundarv line between the areas 



occupied by two species. This is well seen in York- 

 shire, where a hybrid oak is found in the localities 

 in which the sessile oak of the hills comes in contact 

 with the pedunculate oak of the valleys. Hybrids 

 arise frequently in nurseries, gardens, and parks, 

 where several species are cultivated together. 



Hybrid trees are more common than has been sup- 

 posed. Many valuable trees, the real history of which 

 has not been suspected by botanists, are of hybrid 

 origin. As an example, may be mentioned the fine 

 elm, which is universally planted in Holland and 

 Belgium, where it is known as orme gras or Ulmns 

 latifolia, Poederle. This is not, as sometimes imag- 

 ined, a natural species peculiar to those countries. 

 It is unquestionably a hybrid, which is invariably 

 propagated by laj^ers, all the individual trees on this 

 account being uniform in appearance. It seems to 

 have originated three or four centuries ago, probably 

 as a single seedling, which has given rise by vegeta- 

 tive reproduction since to millions of descendants. 



The distinction between sports and hybrids is well 



Mil 



l€t 





Fig. 2. — Holly. Species :— i. Hex Ptrado ; 2. /. Bale- 

 arica; 3,4. I. Aquifoliinn (native). Hybrids: — 5. 

 /. IVilsoni ; 6. /. Hodginsi ; 7. h Hciidersoni. 

 Sports : — The leaves not numbered are those of 

 diflferent sports of the native holly. 



known in the numerous so-called "varieties" of the 

 holly (Fig. 2). Some are sports of Ilex Aqiiifolium, 

 our native holly ; others are hybrids, one parent being 

 the common holly, whilst the other is either Ilex 

 Per ado, which was introduced from Madeira in 1760, 

 or Ilex Balearica, the holly of the Balearic Isles, which 

 was cultivated at Versailles in 1789. Miller, in his 

 account of the hollies in 1750, was acquainted only 

 with the sports, which had arisen from the common 

 hollv, as the other species had not been introduced at 

 that time and hybridisation was impossible. The 

 hybrids originated soon after 1800, the earliest appar- 

 ently being Ilex Hodginsi and Ilex Hendersoni, which 

 were found by Hodgins as seedlings in his nursery 

 at Dunganstown, Wicklow. Here Ilex Perado was 

 cultivated ; and old specimens producing flowers and 

 fruit freely are still common in Wicklow gardens. 

 The holly hybrids are vigorous trees, bearing large 

 leaves intermediate between the parent species. The 

 sports of the common holly are always grafted, and 

 are feeble in growth, with a tendency for single 

 branches to revert occasionallv to the normal form. 



NO. 2358, VOL. 94] 



