178 Elementary Biology. 



We have now completed our examination of the lily, 

 and pass on in the next section to a survey of the points of 

 difference and agreement between it and the buttercup. 

 As already stated, the points of difference are chiefly in 

 external configuration and arrangement of parts, in the 

 arrangement of the tissues of the nbro-vascular strand, and 

 in their mode of secondary growth; and, lastly, in the 

 structure of the embryo. We will devote special attention 

 to these points. It will have been noticed that very little has 

 been said hitherto of the physiology of plants ; that subject 

 is postponed until our consideration of the morphology is 

 completed, since the function of the several structures and 

 the phenomena of nutrition, &c. will be thus more easily 

 understood. The physiology of the several types, moreover, 

 agrees in most essential points, hence by thus postponing 

 our treatment of that subject until we have surveyed all the 

 types we shall escape constant repetition. 



SECTION I V. DICOTYLEDONES RANUNCUL US. 



In selecting a type of the dicotyledonous flowering 

 plants it is advisable to choose one where the various parts 

 are as nearly as possible in a primitive or simple condition, 

 where no parts of the flower are wanting (a complete flower) 

 and where none have been specially modified for purposes 

 connected with cross-fertilisation (a regular flower). The 

 buttercup is a particularly favourable subject for investiga- 

 tion, for it is a complete and regular flower of the penta- 

 merous type. 



Stem. The most important point of difference between 

 the stem of the buttercup and that of the lily is in the 

 arrangement of the fibro-vascular strands. As already seen, 

 they are in the lily arranged irregularly in the fundamental 

 tissue ; in the buttercup they are arranged concentrically. 

 They therefore subdivide the fundamental tissue into a cen- 

 trally placed medulla or pith, and a peripherally placed 



