ABRUPT CHANGES OF LEAF FORMS. 11 



adult forms of foliage liiive long been known in such cases as junipers 

 and eucaly})ts, but these have not been considered as of the same 

 nature as the contrasted inheritance of Mendelian characters. In 

 the case of the cotton and Hibiscus, however, it ai)pears that Mende- 

 lian relations exist in characters that are also subject to abrupt 

 change during individual development. iMendelian inheritance is 

 associated with other contrasted changes in the expression of char- 

 acters. The same characters that show contrasted expression in 

 Mendelian hybrids may be as definitely contrasted, in related plants, 

 in the growth of each individual. ^lendelism, like the dimorphic 

 differences, may be looked upon as representing alternative expres- 

 sion of characters instead of alternative transmission. 



ABRUPT CHANGES OF LEAF FORMS IN HIBISCUS CANNABINUS. 



A very pronounced example of dimorphism of leaves was observed 

 in Eg3^pt, in May and June, 1910, in Hibiscus cannahinus, the so- 

 called Deccan or Ambari hemp, a plant commonly grown along the 

 borders of cotton fields. The object of planting the hemp with the 

 cotton is to avoid the injuries of the plant lice, which are usually 

 severe on the more exposed margins of the fields. Though the hemp 

 plant is a rather close relative of the cotton, it is much less susceptible 

 to the attacks of the insects and grows up more rapidly. The cotton 

 field is protected against the drier outside air that might otherwise 

 enable the plant lice to destroy the outer rows. Moreover, a bast 

 fiber extracted from ♦the Hibiscus is made into a coarse cordage used 

 for many agricultural and domestic purposes. 



Variations of leaf forms in the hemp ])lant show a curious parallel 

 with cotton. In addition to the entire or very broadly lobed leaves 

 comparable to those of ordin^w-y Upland varieties of cotton, there 

 are other varieties with deeply divided narrow leaves, like the so- 

 called ''okra" varieties of cotton in the United States, and some wdth 

 leaves parted to the base into narrow digitate segments, a condition 

 also known in some of the tropical varieties of cotton. (Pis. I, II, 

 and V.) 



Further similarity was found in the fact that the Egyptian variety 

 of Hihiscus cannahinus with the lobed leaves produced entire leaves 

 at the base of the stalk, as also happens with the narrow-lobed 

 "okra" varieties of Upland cotton. The Hibiscus leaves show a 

 very abrupt transition from the broad, simple form of leaves on the 

 lower part of the stalk to the narrow, deeply lobed form on the 

 upper part (fig. 1); this abrupt change in the characters of the 

 leaves seemed the more w^orthy of notice on account of the fact that 

 Mendelian segregation of tlie broad and narrow forms of leaves has 

 been found to occur in the second generation of crosses between 



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