FORM AND STRUCTURE 



Sorosis, is a multiple fruit of which the mulberry is an ex- 

 ample. 



Strobile or Cone, is a multiple fruit consisting of a scale-bear- 

 ing axis, each scale enclosing one or more seeds. Pine 

 cones are examples. 



Galbulus, is a cone, the scales of which liave become succu- 

 lent. The juniper berry is an example. 



The Seed is the fertilized and ripened ovule. It contains the 

 embryo and usually more or less albumen. A well de- 

 veloped embryo possesses four parts : a tiny stem or 

 Caulicle, at the lower end of which is the beginning of a 

 root, called a Radicle; and Cotyledons, wliich are two 

 thickened bodies near the upper end of the caulicle, and 

 between these is a small bud called a Plumule. These 

 parts can be readily seen in the sprouting bean or pea. 

 Some plants produce seeds bearing one cotyledon only ; 

 such are called Monocotyledones. Others bear two co- 

 tyledons, they are called Dicotyledones, 



THE TREE STEM OR TRUNK. 



Stems are of two kinds, Endogenous and Exogenous, so 

 named from the character of their growth. In an endogenous 

 stem the wood is made up of separate threads scattered, here 

 and there, throughout the whole diameter of the stem. In 

 an exogenous stem the wood is collected to form a layer sur- 

 rounding a central column of pith and is itself surrounded by 

 bark. 



A transverse section of a small twig of a tree shows the 

 pith in the centre, around it a zone of wood, then a green 

 inner bark, and finally the outer bark. All parts, except 

 possibly the outer bark, are alive. 



A transverse section of a matm-e tree exhibits a centre of 

 heartwood or Duramen and a zone of sapwood or Alburnum, 

 an inner bark and an outer bark. In addition are seen a 

 series of concentric rings known as rings of annual growth, 

 also a number of hues radiating from centi-e to circumference 

 called Medullary Bays. The pith has disappeared but the 

 medullary rays are composed of pith tissue and form a set 



514 



