438 THE STRUCTURE OF ECONOMIC PLANTS 



taries arise comparatively late in ontogeny, and consist of a ring 

 of papillate cells which are a part of the adaxial epidermis at the 

 base of the calyx. These are bordered by hairs that are stiff and 

 greatly elongated. 



After the divergence of the primordia of the sepals, a common 

 stamen-petal primordium is formed from the rounded mass of 

 meristematic tissue remaining toward the center of the axis. This 

 first develops as a collar-like ring which grows uniformly at all 

 points, but more rapidly at the margin, so that a saucer-like depres- 

 sion is formed surrounded by a thick marginal rim. Five narrow 

 crescentic points, which ultimately differentiate into the petals, 

 arise on this margin alternate with the sepal lobes. Each petal 

 primordium soon develops an apical notch; and, later in develop- 

 ment, the two halves grow at unequal rates. The longer half 

 becomes hairy on both surfaces while the shorter one remains 

 glabrous. It is the interlocking of the hairs of the longer halves 

 that holds them tightly together in the convolute bud. Continued 

 growth of the corolla results in its projection beyond the sepals, 

 and it forms a cone-shaped structure about which the calyx is 

 closely appressed. 



While the petals are forming, the inner margin of the meriste- 

 matic ring, which is the common point of origin of the petals and 

 stamens, continues to grow upward and forms a ridge with five 

 prominent protuberances. This structure is the forerunner of the 

 staminal column, each protuberance producing a fascicle of stamen- 

 primordia; and further development of the five primordial lobes 

 results in the formation of ten paired ridges. The lobes of the 

 staminal column are alternate with the petals, but the growth of 

 the column and the torsion of the petals make it appear that the 

 lobes are opposite them. Gore (i8) has described the subsequent 

 development of the staminal column: 



"soon after the first spherical stamen primordia arise, other primordia 

 appear on top and down the outside face of each lobe of the staminal 

 column, until ten definite rows are formed. Each of these ten rows 

 of stamen primordia, except the bottom members of each row, divides 

 one or more times. Multiplication of stamens by division of existing 

 primordia produces a large number of stamens, from 50 to 1x5 or more 

 in the varieties studied." 



As growth proceeds, the anthers become crowded and closely 

 packed, so that their natural orientation is soon lost, and transec- 



