376 THE STRUCTURE OF ECONOMIC PLANTS 



growing centripetally until they partially or completely divide 

 each locule. The septa are non-ciliate in some forms and pilose 

 in others, the latter condition existing in most non-dehiscent 

 types. 



The Fruit. — The fruit is a spherical or egg-shaped capsule 

 ID to li mm. in diameter and 8 to 15 mm. in height. It is dry 

 at maturity and the partial dehiscence is septicidal, but each locule 

 may also separate into two parts along the line of the dorsal 

 septum so that the ripe fruit seems to be ten-parted. Tammes (ii) 

 reports a variation with respect to dehiscence in flax, it being the 

 general condition in wild species and in a form of cultivated flax, 

 L. usitatissimum crepitans, Boningh., which is still grown in 

 some regions of the Ukraine. In other cultivated forms, the 

 capsule is either non-dehiscent, or only slightly so at the apex 

 of the fruit, and the seeds cannot escape. Two anatropous ovules 

 arise from axillary placentae toward the summit of each locule 

 so that they appear to be suspended. (Fig. 191, A.^ 



The Seed. — The somewhat beaked, oval seeds are flattened or 

 lens-shaped in transection and variable in size, being designated 

 as small or large in commercial practice. In general, the seed 

 of oil flax is the larger, averaging about 5 to 6 mm. in length 

 and X.5 to 3.5 mm. in diameter, while that of fiber flax approxi- 

 mates 3 to 5 mm. and 2. to 1.5 mm. respectively. The smooth 

 surface is highly polished and the seed coat may vary in color from 

 white to various shades of yellow or brown, some being reported 

 as variegated. 



Development of the Seedling. — The germination of the 

 seed is rapid at temperatures of 65-75° F., and the primary tap 

 root emerges in one or two days, constituting the main axis of the 

 root system. The seedling emerges above the ground level in 

 four or five days and the hypocotyl elongates at its basal point, 

 curving until it takes the shape of an inverted U. (Fig. 191.) 

 It pulls the cotyledons and seed coats above the ground, and in 

 about five days, the hypocotyl straightens and the remains of the 

 seed coats are shed. After a period of general growth, there is a 

 zonal elongation of the hypocotyl which is initiated at the ground 

 level and extends progressively upward to the cotyledonary plate 

 until growth in length ceases at the end of 15 to xo days. The 

 first lateral roots appear in five to six days, usually emerging within 

 3 cm. of the soil surface, and most of the subsequent ones originate 



