CHARACTERISTIC FORMS OF LEAVES AND SHOOTS. 



121 



prolongation of the outside of the fig, and bears in consequence a large number of flowers 

 (exogenous lateral shoots). In the nearly related genus Dorstenia the fig remains open ; 

 the margins of the tabular part of the axis which bears the small flowers do not arch over 

 and unite. 



On a process very similar to the formation of the common fig depends the origin of 

 perigynous flowers and of inferior ovaries. Fig. i6o represents this in the perigynous 

 flower of a Rose. / shows the very young shoot which is to develope into a flower, seen 

 half from above and from the outside ; the end of the shoot is thickly swollen ; it has 

 already produced the five sepals / /, and the five petals alternating with them are visible 

 as little knobs, c, between which the apical region of the floral axis appears broad and 

 flat. While the sepals grow quickly, the zone of the tissue of the axis out of which 

 they spring becomes elevated in the form of a circular wall x in //, which afterwards 

 contracts the opening above as seen in IF\ an urn-shaped structure is thus formed 

 which is known under the name of a hip, and is distinguished when ripe by its red 

 or yellow colour and its sweet pulpy tissue. Here also the apical point lies in the 

 middle of the bottom of the hollow, and the inner surface of the wall of the urn is 

 a portion of the outer side of the floral axis which has been turned in. To this cor- 

 responds the acropetal succession of the leaves (which, however, is only adhered to in a 

 general way). It is clear that if the apical point lies ?ity (in 7/), the order of succession 

 of the leaves (in this case stamens st and carpels k) from above downwards must be 

 termed acropetal. 



If an additional proof of what has just been said were wanted, it would be fur- 

 nished by the history of development of the flowers of Geum\ a genus very nearly 

 related to the Rose (Fig. i6i). That part of the floral 

 axis which bears the sepals /, the corolla c, and the stamens 

 a a, is elevated in the form of a circular wall yy\ but 

 the apical region which in Rosa entirely ceases to elongate, 

 becomes here again elevated as a conical body x, bearing 

 at its summit the apical point of the floral axis. The order 

 of succession of the foliar structures is again acropetal, 

 and in consequence the stamens a are formed on the 

 inner side of the axis yy from above downwards, the 

 carpels which succeed them on x from below upwards. 

 In Geum and other Dryadese the urn yy 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 surface becomes the outer surface, 

 in the middle of which the gynophore x rises like a cone, 

 and in Fragaria afterwards swells out, becomes fleshy, and 

 forms the strawberry (a pseudocarp like the hip). 



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

 [that of the subsequently flat receptacle of Geum depends 

 ?on a displacement which is caused by vigorous growth of 

 rmasses of tissue that arise in the form of zones beneath the 

 fgrowing point. 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 and gamosepalous or synsepalous flowers are also not the result of cohe- 

 fcsion; the petals or sepals are on the contrary formed as a whorl of separate pro- 

 [tuberances on the broad end of the young flower-stalk. That a gamopetalous corolla or 

 [gamosepalous calyx subsequently has the appearance of a bell having at its margin only 

 [as many teeth as the leaves of which it is considered to consist, does not depend on 

 flateral 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-shaped part 



Fig. i6i.— Longitudinal section of a 

 young flower of Geum rivale. 



