94 RELATIONSHIPS OF SYMMETRY 



configuration will form the subject of a later chapter, nevertheless I must 

 here point out how instructive is the difference in behaviour of the 

 spruces 1 and the silver-firs. In the silver-firs the lateral buds on the 

 horizontal branches are all laid down from the beginning upon the flanks 

 alone, occasionally in Abies pectinata and other species they appear also 

 upon the under side of the twig ; in the spruces, when they grow strongly 

 in the open and are illuminated on all sides, the higher lateral shoots of the 

 chief stem have a radial arrangement of the twigs, the lower ones alone 

 exhibit a development of buds on the flanks, and chiefly those upon the 

 outer side. This is due to the arrest of the shaded tivigs, that is of those 

 which arise upon the iippcr side, and that this is so is shown by the fact 

 that, so far as I have seen, in spruces grown in close wood, branching from 

 the flanks alone takes place also in the higher lateral twigs. Thus here 

 again we see that in one plant outer influences bring about a relationship of 

 configuration which exists in others from the beginning and is hereditary. 

 As a kind of transition between the two sets of cases just referred 



FIG. 50. Vaccinium Myrtillus. To the left a transverse section through the terminal bud of a subterranean 

 stolon ; to the right a transverse section of an axillary bud which has developed on a plagiotropous shoot of a plant 

 in darkness ; the position of the leaves is not distichous. 



to I may now describe the case of Vaccinium Myrtillus (Figs. 50, 51), 

 which I have found to be as follows 2 : 



The seedling of the whortleberry forms at first an orthotropous 

 radial shoot bearing foliage-leaves with a divergence somewhere about |, 

 but which I have not accurately determined. This shoot has limited 

 growth and its terminal bud is arrested. Lateral shoots arise upon it 

 which develop in part as stolons piercing the ground and bearing only 

 scale-leaves, partly as aerial shoots which are radial like the stolons 

 and have limited growth. The stolons after a time appear above ground 

 and then behave like orthotropous shoots ; only their lateral shoots 

 of higher order become plagiotropous and distichously-leaved and 

 produce again shoots which are like themselves. Examination of one 



1 See also Herbert Spencer, Principles of Biology, ii. p. 132. 



" See also Hofmeister, Allgem. Morphologic, p. 627. I do not find the facts to be altogether as 

 stated by Hofmeister. I cannot agree that the leaves of ' all aerial leaf-buds are arranged dis- 

 tichously.' The behaviour of the orthotropous radial shoot of the seedling shows that this is not so. 

 Compare the analogous case of Lycopodium complanatum, described on p. 103. 



