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THE AMERICAN NATURALIST [Vol. XLIV 



quite similar in both groups of hybrids and presented 

 forms and measurements intermediate between the two 

 parents. The flowers, however, were decidedly smaller 

 than the mean, and resembled those of the female muricata 

 parent although about twice as large. The hybrids then 

 as regards habit and foliage fell in about equal propor- 

 tions into two groups, with greater resemblances to one 

 or the other of the two parents. They presented an ad- 

 mirable illustration of the type of crosses called by De 

 Vries 3 "twin hybrids", and reported for crosses between 

 the Onagra group and Lamarckiana, or one of its deriva- 

 tives, when these latter furnish the pollen. 



These hybrids when self-pollinated set an abundance 

 of seed which germinated readily, in sharp contrast to the 

 experience recorded above for the hybrids of gigas X 

 Lamarckiana. De Vries ('086, p. 761) reports that 

 hybrids of this cross as well as of the reciprocal have 

 proved entirely sterile in his cultures. The fertility of 

 my cross is especially interesting since we are dealing 

 with a hybrid one of whose parents {gigas) has twice as 

 many chromosomes as the other. A large proportion of 

 the pollen grains, 75 per cent, or more, was abortive ; the 

 normal grains were almost wholly of the 3-lobed form 

 (as in muricata), 4-lobed examples being uncommon. 



3. muricata X grandiflora. There were two cultures 

 of these hybrids based on two muricata parents from 

 Woods Hole, pollinated, however, from the same grandi- 

 flora plant which was used in the crosses of biennis 

 and grandiflora, a plant which is described somewhat 

 fully below. The cultures comprised twenty-nine plants 

 which did not pass through conspicuous rosette stages in 

 the hot houses, but quickly developed the main stems, 

 which were 1-2 dm. high when the plants were set out in 

 the garden. Somewhat later these young plants with 

 main stems 4-6 dm. high presented clearly a foliage inter- 

 mediate between the parent types in form, color and tex- 

 ture. Thus the leaves were narrower, thicker, and a 



»De Vries. H. ( '07), "On Twin Hybrids," Bot. Gas., XLIV., 401, 1907. 

 ('08a), "Ueber die Zwillingsbastarde von (Enothera nanella," Ber. deut. 

 bot. Gesell., XXVIa, 667, 1908. 



