40 



DE. E. E. GATES— CONTRIBUTION TO A 



evolutionary unit is here not a series of pure, self-fertilizing biotypes, but a population of 

 interbreeding races whose constituency is changing within limits from generation to 



generation. 



The two series of forms — open-pollinating and self-pollinating — are, however, not 



nearly so sharply separated as was formerly supposed. Later in the present paper I 

 shall cite several cases in my cultures, of the appearance of small-flowered, short-styled, 

 and hence self -pollinated plants from large-flowered, long-styled ones. I have even 

 found several cases of transition from long-styled to short-styled flowers or vice versa^ 

 sufficient to cause the change from open-pollination to close-pollination, on the same 

 plant. All such cases probably occur in hybrids between long-styled and short-styled 

 forms. They are similar to the cases cited by Boulenger (1907). Since species are 

 known having large flowers and short styles (0. Simsiana as well as O, hremstylis^ in 

 which the stigma is more or less rudimentary), and having small flowers with long 



style (0. ornata), it is evident that in the further light of the experimental evidence of 

 transition referred to above, any sharp cleavage-line between open-pollinated and close- 

 pollinated forms, such as was formerly thought to exist, disappears. Added evidence is 

 furnished by the large-flowered, long-styled 0. grandijlora, and its segregate, the small- 

 flowered, short-styled O. Traci/i, which otherwise clearly resembles O. grandiflora. 

 These grew together in Alabama and must have occasionally intercrossed. 



I am growing the second generation of a number of distinct races of O. hiennis from 

 various sources. They differ chiefly in leaf-characters and will be described in detail 

 at another time. The race of O. hiennis which I have used in my hybrid crosses has 

 already been described (MacDougal, 1905, p. 9), but I must add here certain photographs 

 which are necessary for a comparison of the parents with the corresponding parts of their 

 hybrid offspring. PI. 4. fig. 50 represents a typical rosette of this race ; PI. 4. fig. 51, 

 a flowering shoot ; and PI. 4. fig. 52, the same in fruit, to show the capsules and the size 

 and other characters of the bracts. In PI. 4. fig. 53 several buds are represented, reduced 

 in size. Three of them, taken from different heights of the stem, show the great range of 

 continuous variation in the size of bracts of an individual. 



0. muHcata, Linn. 



This Linnean species has usually been distinguished from O. biennis by its smaller 



flowers and narrower leaves. But, as mentioned elsewhere (Gates, 1911 d, p. 580), 



I have found certain races having the flower-characters of 0. muricata {i. e.^ smaller 



than Uetmis)t but with broad leaves. The narrower leaves of O. muricata, as a distinction 



from O. UenniSt therefore breaks down and there alone remains the difference in size of 

 flower. 



The fact that 0. muricata possesses both narrow-leaved and broad-leaved races, and 

 that both f req^uently occur in the same locality and are probably derived from seeds 

 of the same individual, is one of the most interesting discoveries in connection with my 

 cultures of this group. For the broad- and narrow-leaved individuals differ in the same 



