222 MORPHOLOGY OF MEMBERS. 



therefore never consisted of distinct leaves, but is the common basal piece which is 

 developed from the floral axis as a whole, and which shows at its margin the original still 

 separate leaves as teeth of the bell. The reverse is the case in the leaf-sheaths of 

 Equisetum, where an annular wall originally projects round the axis, from which the 

 separate leaf-teeth afterwards grow out. In this case also the sheath cannot be con- 

 sidered as formed by the cohesion of previously distinct pieces, but the separate teeth 

 of the sheath must rather be considered as branches of a single annular rudimentary leaf. 

 A similar explanation applies to the bundles of stamens which are generally termed 

 coherent (monadelphous, polyadelphous, &c.) stamens. As many protuberances are 

 formed originally as there are bundles of filaments to be produced; and these pro- 

 tuberances must be considered as the original staminal leaves which subsequently 

 produce by branching a larger or smaller number of stalked anthers (as e.g. in Hypericum, 

 Callithamnus, &c.). Cohesions of parts originally distinct are rare ; examples are fur- 

 nished by the connate inferior ovaries of two opposite flowers of an inflorescence in 

 Lonicera alpigena, the fruits of Benthamia fragifera which cohere into a large pseudo- 

 berry, and the cohesion of the two stigmata in the flower of Asclepias to each other and 

 to the anthers. The anthers of Compositae are not truly coherent, but only glued 

 together by their sides. 



Much more common than actual cohesion is the abortion of members already 

 formed. Thus, for instance, the paripinnate leaves of some Leguminosae^ originate as 

 imparipinnate leaves ; the terminal leaflet which is finally aborted is at first in the bud 

 even larger than the lateral leaflets ; but, as development progresses, it is so retarded 

 that in the mature leaf it overtops the origin of the uppermost lateral leaflets only as a 

 minute point. In the same manner the whole (branched) leaf-blades of many Acacias 

 are also abortive, and are replaced by the petiole (phyllode), which is then expanded 

 in its median plane. Still more complete is the abortion of the leaves from the axils of 

 which spring the branches of the panicles of Grasses ; and in this class whole flowers 

 are often aborted. In diclinous Phanerogams the unisexuality of the flowers 

 usually depends on the abortion of the stamens in .the female, of the carpels in the 

 male flowers. Sometimes only one of several stamens is aborted, as in Gesneraceae 

 {e. g. Columnea, where it is transformed into a small nectary) ; and the same occurs 

 with the carpellary leaves {e.g. in Terebinthaceae). In all these cases the structure which 

 is afterwards abortive is actually present in the bud or even later, but its further 

 growth ceases. The comparison, however, of nearly related plants shows that very 

 commonly certain members are wanting in the flower the presence of which might 

 be expected from the position and number of the others and from their presence 

 in nearly related forms, although in such cases even the earliest condition of the 

 bud does not exhibit a trace of the absent member. Since from the point of view 

 of the Theory of Descent it must be assumed that nearly related plants are descended 

 from a common ancestral form, the absent member may in such cases also be sup- 

 posed to be aborted, only the arrest of development which has once taken place at an 

 early period is so complete and has become so hereditary, that even its first rudiment 

 is suppressed. The true theory of the structure of many flowers, and the reference 

 of diff"erent forms of flowers to common types, often depends on the restoration of 

 aborted members of this kind; but to this we shall recur in detail in Book II, when 

 treating of Phanerogams. 



Sect. 29. Reproduction; Sexual Organs ; Alternation of Generations. 



Reproduction, or the production of new individuals, is generally brought about 

 by particular portions of an individual becoming detached, which then have the 

 power, first of all of producing new organs of nutrition, and afterwards of continuing 



^ Hofmeister, Allgemeine Morphologic, p. 546. 



