GOSSYPIUM 437 



Floral Development. — The ontogeny of the flower has been 

 investigated by Doak (ii, ii) and Gore (i8). In the development 

 of the floral organs from the meristem of the terminal bud, the 

 primordia of the involucre, calyx, corolla, androecium, and gynoe- 

 cium arise in acropetal succession. The three bracts of the involu- 

 cre appear very early in ontogeny as crescentic primordia, the first 

 one arising opposite the leaf, and the other two following in suc- 

 cession. At first, the margins of the bracts are entire, but early in 

 their development they become serrate. They increase rapidly in 

 size; and, at maturity, form a triangular bud within which the 

 floral organs deveJop until anthesis, when the unfolding petals 

 force the bracts apart. Following anthesis and the shedding of all 

 the flower parts, except the pistil and calyx, the bracts return to 

 their original position so that a young fruit may have the out- 

 ward appearance of a large bud. 



The extra-floral nectaries of the involucre are formed compara- 

 tively late in its development. The three outer ones, which are 

 located at the base and on the outside of the involucral bracts, occur 

 in all American species of cotton, although they are not necessarily 

 present in every flower. They are somewhat larger than the leaf 

 glands, forming rounded or pear-shaped pits from the floor of which 

 arise round secreting cells. The three inner involucral nectaries 

 which are present in most species of cotton are located between the 

 calyx and involucre and alternate with the outer ones. The inner 

 nectaries are shallow and usually naked in the case of American 

 species, but in Old World cottons may be protected by a covering 

 of short stellate hairs. 



The primordium of the calyx arises next; and, at first, forms an 

 undulating ring of meristematic tissue. As this grows upward, 

 five crescentic protuberances are diff^erentiated which ultimately 

 become the tips of the five-lobed gamosepalous calyx. The lobes 

 of the calyx incline over the floral axis, and, for a time, enclose 

 the primordia of the other floral parts. Further development of 

 the calyx results in the formation of a shallow cup with a con- 

 stricted throat and an undulating rim. Inequalities in the rate of 

 growth at the apex and base of the calyx result in the dilatation of 

 the basal portion of the tube while the throat of the calyx fits 

 tightly over the structures within. Later, there is a reversal in 

 the growth rate of the upper and basal regions; and, at blossoming 

 time, the throat of the tube is greatly enlarged. The floral nee- 



