ARRANGEMENT OF LEAVES. 9 



whole number of vertical ranks of leaves. The fraction as a whole 

 indicates the part of the circumference of the stalk included between 

 two successive leaves of a spiral. The most frequent arrangement of 

 the leaves of the cotton plant is in the three-eio:hths spiral. This means 

 that the leaves stand in eight ranks, that three turns around the stem 

 are made by the sphal in passing from any particular leaf to the next 

 that is directly al)ove it, and tliat successive leaves along the spiral 

 are separated by three-eighths of the circumference of the stalk. 



NEW WORLD COTTONS WITH THREE-EIGHTHS SPIRALS. 



The arrangement of leaves in three-eighths spirals appears to be a 

 normal characteristic of all pure strains of cotton belonging to the 

 Upland and Sea Island species (Gossijpium hirsutum and G. harbadense) 

 and to the nearly related types that are natives of tropical America. 

 This normal arrangement appears with much regularity in varieties 

 introduced from tropical America, when i)lanted for the first time in 

 the United States. With the advance of acclimatization, the leaf 

 arrangements are varied by frequent examples of one-third and two- 

 fifths spirals, and similar irregularities are found among native Upland 

 varieties. Pure stocks are much more likely to have the regular 

 tliree-eighths arrangement than tliose not carefully bred. 



Variations in the arrangement of the leaves were first noticed in 

 Egyptian-Upland hybrids, but were found later in all hybrid stocks, 

 including many crosses between different Upland types. Hybrid 

 jilants lUxay have a one-third, two-fifths, or even a five-thirteenths 

 spiral arrangement, although both parents may have had the normal 

 tliree-eighths arrangement, or hybrids may have the normal arrange- 

 ment of the parents. The very general prevalence of the tliree- 

 eighths spiral among American types of cotton warrants the suspicion 

 that any plant without the normal tliree-eighths arrangement is of 

 hybrid origin or the result of recent mutative variation. 



On the other hand, there is a possibility that the regularity of the 

 three-eighths arrangement in the newly imported stocks ma}' rep- 

 resent one of the tendencies of reversion that are very frequently 

 sho^vn in other characters of the plants. The simpler forms of spirals 

 may be correlated with the smaller size and more fertile habits of 

 growth of acclimatized stocks, but if this be true some varieties should 

 be found with the simpler spirals as a regular feature. The systems 

 of arrangement followed by the foreign cottons in their native coun- 

 tries must also be ascertained before definite conclusions can be dra\^^l 

 regarding the effects of new conditions and acclimatization. 



Mutative stocks, as far as known, differ fi-om hybrid stocks in that all 

 the plants of a stock have the same leaf arrangement. This may be 

 like the stock from which the type mutated or it may be different. 

 The only type of Upland cotton that seems to show a regular deviation 



