CHARACTERISTIC FORMS OF LEAVES AND SNOOTS. 



201 



Fig. 153. — Longitudinal section of a 

 young flower of Geum riiiale. 



as a conical body jf, bearing at its summit the apical point of the floral axis. The 

 order of succession of the leaf-structures is again acropetal, and in consequence the 

 stamens a are formed on the inner side of the axis y y 

 from above downwards, the carpels which succeed them 

 on .V from below upwards. In Geum and other Dryadeae 

 the urn y y spreads out at the time of fertilisation, its 

 margin grows so vigorously in size that it expands in the 

 form of a flat plate, and after the expansion its inner sur- 

 face becomes the outer surface, in the middle of which 

 the gynophore .v rises like a cone, and in Fragaria after- 

 wards swells out greatly, becomes fleshy, and forms the 

 strawberry (a pseudocarp like the hip). 



It will be seen that the formation of the fig„the hip, and 

 the subsequently flat receptacle of Geum depends on a 

 displacement which is caused by vigorous growth of masses 

 of tissue that arise in the form of zones beneath the 

 pimctum vegetationis. There is in these cases no such thing 

 as adhesion of foliar structures (as is usually stated in works 

 on descriptive botany). The so-called coherent corolla 

 and calyx of gamopetalous or sympetalous (as well as 

 gamosepalous or symsepalous) flowers, are not the result 

 of cohesion ; the petals (or sepals) are on the contrary 

 formed in a whorl on the broad end of the young flower- 

 stalk as isolated protuberances. That a gamopetalous 



corolla or gamosepalous calyx subsequently has the appearance of a bell having at its 

 margin only as many teeth as there should be leaves, does not depend on lateral 

 cohesion of the margins of the leaves, but on the fact that the whole annular zone of 

 the young receptacle which bears the corolla (or calyx) grows up ; the bell-sliaped part 

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

 formed out of the floral axis as a whole, and shows at its margin the original still isolated 

 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 shoot out. In this case also the sheath cannot be considered as 

 formed, by the cohesion of previously isolated 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 stamens ; there are, in fact, as many protuberances formed originally as there 

 are bundles of filaments to be produced. These protuberances must be c )nsidered as 

 the original staminal leaves which subsequently produce by branching a larger or smaller 

 number of stalked anthers (as e. g. in Hypericum, Callithamnus, and many others \ 

 Cohesions of parts originally isolated are, as a rule, rare ; examples are furnished by 

 the coherent inferior ovaries of two opposite flowers of an inflorescence in Lonicera 

 alpigena, the coherent fruits of Benthamia fragifera which grow to a large pseudo-berry, 

 and the cohesion of the two stigm.ta in the flower of Asclepias to each other and to 

 the anthers. The anthers of CompositcC 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 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 highest lateral leaflets only as a minute point. In the 



Hofmeister, Allgemeine Morphologic, p. 546. 



