128 MANUAL OF BOTANY 



in analysing some of the eymose ftirms. The diohasium most 

 frequently occurs together with verticillate, and particularly 

 opposite decussate leaves. A polyohasiimi may result from the 

 suppression of an internode in each successive branching, the 

 result being that instead of two, four axes of the dichasium arise 

 together, the two younger being at right angles to the two older. 

 In the Elder (Sambucus) there are apparently five such axes, 

 springing from the same point, thus simulating an umbel. The 

 five axes consist of the primary one and two successive pairs, 

 which are severally somewhat distorted in growth ; each axis 

 bears several subordinate ones, which maybe similarly arranged, 

 and each ultimately bears several flowers. 



In some helicoid cymes, the flowers, which are seated on the 

 convex side of the curved sympodium, arise in two ranks instead 

 of one. This has been explained as a unilateral raceme, but 

 there appears to be little doubt that its true nature is oymose. 

 The appearance of two ranks of flowers is explained by Eichler 

 on the ground of antidromy. The phyllotaxis in such cases is 

 spiral, and the genetic spiral, instead of passing regularly from 

 right to left round the axis, becomes reversed in the successive 

 parts of the sympodium, travelling in the first from right to left, 

 in the second from left to right, and then again reversing its 

 direction. Examples are seen in many of the Boraginacese. 



It is held by some botanists that in a few of the plants of the 

 last-named natural order, where the inflorescence is ajiparently 

 a helicoid cyme, or a unilateral raceme, the branching of the 

 successive axes is not lateral but diohotomous, the growing 

 point of each axis after the first dividing into two equal parts ; 

 one of the resulting branches speedily terminates in a flower, 

 while the other again dichotomises. 



S. THE FLOWER. 



The term flower may be applied to any shoot which is spe- 

 cially modified in connection with spore-production. The term 

 is usually, but erroneously, restricted to the Phanerogams, 

 in which this modification results in a structure generally of 

 peculiar form and often of great beauty and fragrance. Flowers, 

 however, of a lower type of complexity than these can be 

 recognised in the Cryptogams. The common Horsetail {Equise- 

 turn) has its sporangia arranged upon a niimber of peltate 

 sporophylls which are aggregated in the form of a cone at the 

 apex" of certain shoots {fl.g. 243). These constitute a, flower 



