l82 



MORPHOLOGY OF MEMBERS. 



diaceae always arise so near to the apex, and they assume at so early a period the 

 character of dichotomies developed in a bifurcate manner, that, until further inves- 

 tigation proves the contrary, they must be considered as such. It is scarcely necessary 

 to mention in conclusion that when roots branch dichotomously the bifurcations are at 

 first covered by the original root-cap, as is shown in Fig. 138. 



(c) Lea-ves. Bifurcations resulting apparently from true dichotomy occur in the leaves 

 of some Ferns, e.g. Platycerium alcicorne^ ; and, according to an older statement of 

 Hofmeister, it appears that the branching of Fern-leaves generally commences dicho- 

 tomously, although mature leaves mostly resemble a monopodium. On a mid-rib 

 forming a continuation of the petiole are placed numerous secondary mid-ribs with 

 secondary laciniae (pinnae). Since these branches are apparently always alternate and 

 not opposite, and the terminal lobes of the leaves are frequently developed as equally 

 strong bifurcations, leaves of this kind may be considered, according to Hofmeister's 

 hypothesis, as dichotomies developed in a sympodial (and indeed a scorpioid) manner, 

 the mid-rib representing the sympodium, and the apparent lateral branchlets the weaker 



Fig. 138. — Dichotomy of the root of Isoeies l^Kiistris (after 

 Hofmeister) (x 400); 1 1' the apical cells of the branches; wh 

 the old root-cap formed before the bifurcation ; wA2 the two 

 root-caps of the branches, sti 1 covered by the former one ; e 

 epidermis ; / parenchyma ; tyfibro-vascular bundle of the root. 



Fig. 139. — Part of a male Rov/er oi Rtcinus cotnrnunis 

 cut through lengthways ;yy the basal portions of the com- 

 poundly branched stamens ; a their anthers. 



branches (as in Fig. 134, C, p. 178) ; a process which is repeated in the segments of the leaf 

 itself when the leaf is doubly or many times pinnate. A similar interpretation may per- 

 haps be permitted of the simply pinnate leaves of Cycadeae. The repeated branching 

 of the stamens in the male flowers of Ricinus appears, according to Payer ^, to proceed 

 from dichotomy, and to a certain extent even from polytomy, commencing at an early 

 period. The separate stamens appear as roundish protuberances on the floral axis, and 

 each of these immediately forms two or more similar protuberances on its surface, and 

 on these the same process is again repeated. When mature, the stamens (Fig. 139) 

 appear as if divided dichotomously or trichotomously upon long stalks, the branches 

 being developed somewhat irregularly. 



* The petiole of Adiantum pedatum divides above into two equally strong branches, each of 

 which forms a helicoid cyme of ramifications arising probably by dichotomy ; the weaker branches 

 of the helicoid cyme stand upright and their numerous pinnce form a scorpioid cyme produced 

 by further dichotomy. This is one of the most beautiful forms of leaves, the history of the 

 development of which would be of unusual interest. 



^ Payer, Organogenic de la fleur, pi. 108, cor.finned by Warrhing /. -. 



