PARAI.LKF. LKAF FORMS IN COTTON. 



19 



house plants of Eirvptiaii cotton have manv ot the leaves of the 

 fruiting branches quite simple, a cliaracter that appears very seldom 

 in open-air plants. A comparison of figure 12 with figure 14 will 

 give an idea of the range of variation in leaf forms on the fruiting 

 branches of the Egyptian cotton and of the extent to which the 

 expression of the characters may be modified by external conditions. 

 It may also be noted that the entire leaf of the Egyptian cotton 

 grown un(U>r greenhouse conditions is l)roader and less pointed than 

 that of theUplantl cotton grown in Texas under open-air conditions. 

 As the figure also shows, the texture of the entire Egyptian leaf is 

 much more delicate than that of the Upland loaf, which is not true 

 in outdoor plants of Egy])tian cotton. 



The greater tendency of the Egyptian cotton to produce entire 

 leaves is also apparent 

 in the early stages of 

 growth. Lobed leaves 

 develop on young plants 

 of Upland cotton from 

 lower joints than in 

 Egyptian cotton, as al- 

 ready noted. Hybrids 

 between Upland and 

 Egyptian cotton, grown 

 at Bard, Cal., in 1911, 

 were intermediate in this 

 respect and usually be- 

 gan to show lobed leaves 

 on the third joint above 

 the cotyledons. The 

 transition from the en- 

 tire to the lobed form of 

 leaves was much more 

 gradual among the hy- 

 brids than in })ure Egyptian j)lants. Very large luxuriant seedlings of 

 the Egyptian cotton, with vegetative branches alreatly pushing from 

 the nodes of the cotyledons, seemed to show less definite transitions in 

 leaf form than the somewhat smaller and more normal plants where 

 the buds in the axils of the cotyledons had remained dormant. Fail- 

 ure of the normal specialization of leaf forms would correspontl with 

 abnormalities in the formation of the branches that occur very fre- 

 quently in the Egyptian cotton under comlitions of too luxuriant 

 growth. 



221 



Fig. 8. 



-Mature leaf of "King" Upland cotton, parent of "okra- 

 leaved" variations. (Natural size.) 



