HETEROMORPHISM. 47] 



leaving a scar. Thus we see the shoots of a plant-body are variously modifie-l 

 and we may speak of a heteromorphism in this connection analogous to thui 

 existing amongst the polyps of a coral. 



It not infrequently happens, amongst purely foliage-shoots, that the lateral 

 shoots (or anaphytes) bear foliage quite unlike that borne by the shoot that gives 

 them origin. In many perennial shrubs and trees a long series of asexual shoots 

 arises, of which the lowest and highest are so different, that one might easily 

 suppose them to belong to different species of plants; or that a gardener had 

 grafted a bud of another species upon the plant. The shoots of young Ivy plants 

 (Hedera Helix), whether creeping on the soil of the forest-floor, or climbing up 

 the trunks of trees or steep rock-faces, bear shortly -lobed, white- veined, dull- 

 looking leaves, and produce a large number of attachment-roots which hold the 

 shoot to the substratum. The shoots of an old plant, however, developed high 

 up on the tree crown, or over the top of the wall, bear bright shining, heart- 

 shaped leaves without conspicuous veins, nor do they produce roots at all. It 

 is this latter class of shoots alone which bring forth flowers; the creeping shoots 

 never do so (cf. vol. i. p. 709). 



This contrast between the appearance of the shoots of a young plant and those 

 produced in later years is much more marked in the Aspen (Populas tremula). 

 The foliage-leaves of the first year's shoots are triangular, cordate at the base, 

 and only shortly stalked, they are also hairy on the under surface; those arising 

 on the shoots of a thirty -year-old Aspen are circular in outline, smooth on both sides, 

 and provided with long petioles. Similar is the case of many Willows, Oaks, and 

 Myrtacese; in the last-named family the Australian Eucalyptus globulus is worthy 

 of mention. The leaves on its first year's shoot are sessile and cordate at the base, 

 whilst on the grown tree they are stalked and curved like a boomerang. Very 

 marked, again, are the differences in the character of the foliage-leaves on the 

 successive shoots of the Junipers (e.g. Juniperus excelsa, japonica, phcenicea, 

 chinensis, and Sahina). The leaves on the younger branches (for the first ten 

 years about) are acicular, stiff and spreading; those on the shoots of later years 

 are short, scale-like, and closely imbricating. Worthy of note in this connection 

 is the contrast of long and short branches seen in many Conifers, e.g. the Larch 

 (Larix). Though the actual leaves are not dissimilar, their insertion is, and the 

 length of the shoots producing them. Whilst the short branches do not attain 

 a greater length than 1 centimetre, the long branches reach to 15 or 25 cm.; 

 to this contrast is due in large degree the altogether peculiar physiognomy of the 

 Larch-tree, as shown in fig. 354 (cf. also, fig. 337 \ p. 443). 



The fruit-trees in our orchards are some years covered with blossom, and, 

 with a propitious summer, they are weighed down with fruit in the autumn. 

 Such "bumper" years are generally followed by a series of lean years, in which 

 little fruit is ripened, or flowers are hardly produced at all. The same thing 

 is observed in forest trees. There is a saying that Firs and Larches only form 

 their cones in plenty once in seven years. This is so far right in that a good 



