GROWTH OF ENDOGENS. 



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consequently called Endogenous. These have neither pith, 

 rays, nor concentric circles, nor any bark, properly so called, 

 only an outer skin. The bole of an endogenous tree consists 

 of a number of woody cells, interspersed with bundles of 

 fibres ; and as the stem lengthens, the leaves on its summit 

 send down more woody fibre, so that the tree becomes more 

 closely filled round the margin of the trunk, and the heart- 

 wood remains light ; on this account the wood of these trees is 

 of little value as timber (fig. B). The outer skin is capable of 



A ^ B 



A Transverse section of the stem of an Endogenous tree. 

 B Longitudinal section of the stem of an Endogenous tree. 



distention, so that the tree bole does increase in size to some 

 extent, and the remains of the footstalks of the leaves help it 

 to increase in height, while the new leaves of each spring send 

 down fresh fibre to the trunk. 



The third great class, the Lobeless, increase only by growing at 

 the top : hence they are called Acrogenous or summit-growers. 

 But we will not enter upon them at present. Our business of 

 to-day lies with the One-lobed class, with their horizontally- 

 veined leaves and inward-growing stems. Unfortunately our 

 British plants of this class are almost entirely humble herbs. 



The first order in the One-lobed class is the Petaliflors. 

 Though characterised as thus, the petals are not always present, 

 but the parts of the flower are arranged in a circular form, 

 and the presence of petals seems to be provided for. 



