34* 



FOURTH GROUP. SEED-PLANTS. 



especially if they are numerous, can be readily seen to be arranged one above another 

 in alternate whorls or ascending spirals ; in the Angiosperms, on the contrary, 

 that portion of the floral axis which bears the floral envelopes and sporophylls 

 is so abbreviated, that space has to be obtained for the insertion of the different foliar 

 structures by a corresponding expansion or increase in circumference of the torus ; 

 this swells out into the shape of a club both before and during the formation of the 

 floral leaves, and is not unfrequently flattened like a disk or even hollowed out into a 

 cup in such a manner that the apex of the floral axis occupies the lowest point in the 

 depression, while the cup encloses the carpels, as in the perigynous flowers, or even 



takes part in the formation of the 

 ovary which in this case is inferior 

 (Fig. 268). The effect of this as 

 regards the outward aspect of the 

 flowers is that their parts do not 

 usually appear to be arranged one 

 above another, but in concentric 

 circles or in scarcely ascending 



spiral lines, and hence the illus- 

 tration of the relative position of 

 the parts of the flowers by dia- 

 grams or ground-plans, such as 

 those which will be explained 

 more fully below, seems especially 

 suitable in the case of the Angiosperms. This abbreviation of the torus is 

 evidently the chief cause also of the unions and displacements which are nowhere 

 found so abundantly as in the flowers of Angiosperms; and since the small 

 development in length of the floral axis itself arises- from the early cessation of 

 apical growth, even the acropetal succession of the floral leaves may be disturbed 

 by formation of intercalary zones of growth 1 , though even in these cases the dis- 

 turbance of the general regularity is inconsiderable. However the acropetal suc- 

 cession is in most cases strictly preserved, and sometimes the apical growth of 

 the floral axis continues long enough for the foliar structures to be evidently 

 arranged in circles one above the other or in ascending spirals, as is the case, in the 

 Magnolieae, Ranunculaceae, and Nymphaeaceae. Occasionally single sections of the 

 axis are much elongated within the flower, as in Lychnis (Fig. 273) between the calyx 

 and corolla, in Passiflora between the corolla and the stamens, in the Labiatae 

 between the androecium and the ovary. 



The flower of the Angiosperms like that of the Gymnosperms is a metamor- 

 phosed shoot, a leaf-bearing axis ; but the Angiosperms are specially distinguished by 

 the high degree of metamorphosis in the flowering shoot, and by the peculiar 

 characters of the floral leaves and their relative positions, which are quite different 



FIG. 268. Asarum canadense. A a flower in longitudinal section ; 

 p the perianth. B transverse section of the flower above the ovary. 

 C transverse section of the sex-locular ovary. D a stamen with the lateral 

 anthers. 



1 These intercalary zones of growth have the properties of growing points, and new formations 

 arise on them, as in the present case, and in such a manner that the latest is nearest to the growing 

 point; the succession therefore is acropetal or progressive; but new formations may also be inter- 

 posed between the older. 



