146 



are usually without stipules, with a well-developed leaf base 

 and not disarticulating readily from the parent axis. The 

 primary root soon dies and its place is taken by adven- 

 titious roots which arise successively higher and higher on 

 the stem. The collateral, closed vascular bundles are scat- 

 tered irregularly through the stem. Secondary growth 

 in thickness rarely occurs, but when it does and a cambium 

 ring is present, the latter does not form a continuous ring 

 of wood on the inside, but produces closed vascular bundles 

 scattered in fundamental tissue. Perennial stems usually 

 have no distinct bark, no annual rings, and no medullary 

 rays, but possess true vessels. 



Dicotyle- 132. Dicotyledons. Embryo has 



dons. typically two opposite cotyledons which may remain within 



the seed, or become green and appear above the ground in 

 germination. These plants are herbs, shrubs or trees. The 

 ilowers have their parts usually in whorls of 5 or 4. The 

 leaves generally have reticulate venation. The leaves often 

 have stipules, rarely have a conspicuous sheathing leaf-base, 

 and usually disarticulate freely from the parent axis. The 

 primary root usually persists to form a tap root. The collateral, 

 open vascular bundles are arranged in a circle. Secondary 

 growth in thickness takes place in perennial stems by means 

 of a complete cambium ring which continually forms woody 

 tissue on the inside and cortical tissue outside. Perennial 

 stems usually possess distinct bark, annual rings, medullary 

 rays and numerous vessels. 



Synopsis of 133. The following Key will now 



theSub-divi- help us to bring into focus the principal groups of the Vegetable 

 which we have considered above : 



Kingdom. 



CRYPTOGAMS. Plants not forming true seeds. 



(" Algae . . Plants contain- 



THALLOPHYTA. ing chloro- 



phyll, chiefly 

 aquatic. 

 Cellular plants with no differentia- -^ Bacteria. - Very^ 



tion into stem and leaves. An 



altogether wanting or irregular. 



minute plants i Colourless plants 



alternation of generations is multiplying by L without 



splitting. i chlorophyll. 



L Fungi. J 



