138 



ORGAKOGRAPHT. 



laws, the determination of those laws must be considered to be a 

 matter of much importance. It has been supposed by some 

 that the arrangement of the leaves varies in the different classes 

 of plants : thus, that in Dicotyledons where the cotyledons or 

 first leaves which are developed are opposite, that the regular 

 arrangement of the leaves in such plants is to be opposite or 

 whorled also, and tliat when they become alternate, this arises 

 from the prolongation or extension of the nodes: while in 

 Monocotyledons on the contrary, which have but one cotyledon 

 usually, or if more than one, then placed alternately, that the 

 regular position of the leaves is alternate also, and that when 

 they become opposite or whorled, that this arises from tlie non- 

 development or shortening of the successive internodes. The 

 investigations however of Bonnet nearly a century ago tended 

 to prove that all leaves and their modifications have normally a 

 spiral arrangement on the stem; and he was led to this belief by 

 observing that if a line be drawn from the bottom to the top of 

 a stem, so as to touch in succession the base of the different 

 leaves upon its surface, it would descril)e a spiral around it; he 

 found also, that the relation of the leaves to each other was 

 constant, each being separated from tlie other by an equal dis- 

 tance, so that if we started with any particular leaf and waited 

 until 'another leaf Avas reached which corresponded vertically 



Fig. 266. 



with it, and then proceeded to the 

 leaf beyond this, we should find that 

 tliat would also correspond vertically 

 with the one next above that which 

 we started from, and so on each leaf 

 as it succeeded the other above would 

 be placed vertically over one of the 

 successive leaves below, but that in 

 all cases in the same plant the num- 

 ber of leaves between the one started 

 from, and that which corresponded 

 vertically with it was always the 

 same. Thus if we take a branch of 

 the Apple or Cheny-tree {Jig. 266), 

 and commence with any particular 

 , , leaf which we will mark 1, and then 



f7o. 2fi( . A portion of a branch of , , ^. . 



a Cherrytrtc. witl> six leaves. prOCCcd UJJWards COnnCCtUlg HI OUr 



the sixtii of which is placed coursc the baso of succccdiug loaves 



vertically over the first. Tlic , ,. • c . • in 



ri>?ht-l.an(l (iKure iathe same by a IniC, Or pjCCC ot Stmig, A\ C Shuli 



branch nuiKiiitied. The numhtTS ti,,,\ tiuit WC shall pasS thc IcaVCS 



indicate the points of insertion , , ^ „ . i r i » *: » , i 



oftheUavea. marked 2 3 4 and 5, but tnat when 



wc rcacii thc one marked 6, that this 



will corn'S])ond vertically with the 1st, and then i)rocccding 



further, that the 7th will he directly over the 2nd, the 8th over 



the 3rd, thc 9th over thc 4th, the 10th over the 5th, and thc 



