DEVELOPMENT OF THE MEMBERS OF ONE BRANCH-SYSTEM. 



163 



outer side again a lobe of the third order, 3 3, which again produces a similar one of the 

 fourth order, 4 4, and so on. According to the general definitions given above, the first 

 branch of the leaf, i, forms with 22a dichasium ; but each branch of the dichasium de- 

 velopes further only on one side, the new branches always arising either only on the left 

 or only on the right side, 3 from 2 and 4 from 3 ; every lateral branch thus produces a 

 sympodial system, and in fact a helicoid cyme. 



If now the basal pieces 2, 3, 4, on both lateral shoots combined in a sympodial manner 

 are imagined to be much shortened, so that the bases of the lobes 2, 3, 4 come close to 

 the base of the lamina r, then all the lobes of the leaf wnll appear to spring from one 

 point, and the leaf is called digitate or fingered. It would appear, however, that such 

 leaves also arise by the formation from the broad end of the young leaf itself first of a 

 middle lobe, and then of new^ lateral lobes right and left from above downwards ; 

 these latter being thus arranged in the order of their origin, as in Lupinus, according 

 to Payer's drawings (Organogenic de la fleur, pi. 104^. If the lobes then remain united 

 or have the appearance 

 of a continuous lamella, ^-^^'^^^r--^ /? 



we have a peltate leaf. 

 It is impossible to go 

 more into the detail of 

 these processes without 

 numerous illustrations 

 which cannot be given 

 here. Fig. 134 may, on 

 the other hand, explain, 

 in conclusion, the origin 

 of the quadripartite la- 

 mina of the leaf of iV^/r- 

 silea Drummondi, ac- 

 cording to J. Hanstein's 

 researches'". The leaf 

 has its origin, in this 

 case, in a cell of the 

 vegetative cone of the 

 stem, which, like the 

 apical cell of the leaf, 



produces two rows of segments fr.om which the right and left halves of the leaf are 

 formed. Thus a broad cone first arises, growing at its apex, and bent towards the 

 stem {A, B) ; when this which is the future leaf-stalk has attained a certain height, it 

 increases in breadth right and loft. Beneath the still growing apex, Z), bs, a protuber- 

 ance [stb) arises on both sides ; and while the latter (destitute of an apical cell) becomes 

 still more arched (C, stb) the apical growth of the leaf ceases {C, bs), its apical cell 

 disappears, and soon two equally strong outgrowths arise near the apical -point, which, 

 like the earlier lateral ones, increase vigorously and grow out into broad lobes of the 

 leaf. Thus arises a quadripartite lamina at the end of the leaf-stalk, the lateral lobes 

 of which have resulted from lateral branching, but the middle ones by dichotomy. 

 When more fully developed the four lobes remain small at their base, becoming much 

 broader at the free margin ; and, since the part of the leaf from which they originated 

 remains short and narrow, they appear, in the mature leaf, to spring from a single 

 point, the end of the leaf-stalk. 



(d) Branch-system of Leaf-forming Shoots. The branching of the stem of Lyco- 



I" ir,. I :(4.— Development of the leaf of AfarsiUa Druvimoiidi (after J. Hanstein). A, C, D 

 seen from the inner surface; R lonK'itudinal section vertical to A; bs apex of the leaf 

 q—z the segments of the apical cell ; stb lateral lobes of the lamina in their earliest state. 



^ Compare further Trecul, Formation des feuilles, in Ann. des Sci. Nat. vol. xx. 1853; and 

 Payer, /. c. p. 403 ; Entwickelung der Blattgestalten, Jena 1846. 

 '^ Jahrb, fur wissen. Bot. vol. IV. 



M 2 



