22 



BOTANY 



PART I 



but where the rainfall is evenly distributed throughout the year 

 buds develop no such means of protection. 



Many of the deciduous trees in Temperate regions are inclined to unfold their 

 winter buds in the same vegetative period in which they are produced. This 

 tendency is particularly marked in the Oak, and results in the development of a 



MIDSUMMER GROWTH. 



All the buds of a plant do not develop ; there are numerous deciduous trees — 

 such as the Willow, in which the terminal buds of the year's growth regularly die. 

 Sometimes buds, usually the first-formed buds of each year's shoot, seem able to 

 remain dormant during many years without losing their vitality ; these are termed 

 dormant buds. In the case of the Oak or Beech such latent buds can endure 

 for hundreds of years ; in the meantime, by the elongation of their connection with 

 the stem, they continue on its surface. Often it is' these, rather than adventitious 

 buds, which give rise to the new growths formed on older parts of stems. It may 

 sometimes happen that the latent buds lose their connection with the woody parts 

 of their parent stem, but nevertheless grow in thickness, and develop their own 

 wood ; they then form remarkable spherical growths within the bark, which may 

 attain the size of a hen's egg and can be easily separated from the surrounding 

 bark. Such globular shoots are frequently found in Beech and Olive trees. 



The Metamorphosis of the Shoot. — The bulbils and gemmae, 

 which become separated from their parent plant and serve as a means 

 of reproduction, are special forms of modified buds. They are always 

 well supplied with nutritive substances, and are of a corresponding 

 size. Many plants owe their specific name to the fact that they produce 

 such bulbils, as, for example, Lilium bulbiferum and Dentaria bulbifera. 



Shoots that live underground undergo characteristic modifications, 

 and are then termed root-stocks or khizomes. By means of such sub- 

 terranean shoots many perennial plants are enabled to persist through 

 the winter. A rhizome develops only modified leaves in the form of 

 larger or smaller, sometimes scarcely visible, scales. By the presence 



of such scale leaves and by 

 its naked vegetative cone, 

 as well as by its internal 

 structure, a rhizome may 

 be distinguished from a 

 root. Rhizomes usually 

 produce numerous roots ; 

 but when this is not the 

 case, the rhizome itself 

 functions as a root. Rhi- 

 zomes often attain a con- 

 siderable thickness and 

 store up nutritive material 

 for the formation of aerial 

 shoots. In the accompanying illustration (Fig. 21) is shown 

 the root-stock of the so-called Solomon's Seal (Poh/goiwtum multi- 

 florum). At d and c are seen the scars of the aerial shoots of the 



Fig. 21. — Rhizome of Polygonatum multifiorum. <>, Bud of 

 next year's aerial growth ; I, scar of this year's, and 

 c, d, e, scars of three preceding years' aerial growth ; 

 roots. (% nat. size.) 



the 



