22 



DR. E. R. GATES— CONTEIBUTION TO A 



longer and narrower than (2), usually mucli crinkled, pointed, the blade narrowed 



6 



dually to a petiole with irregularly lobed or jagg-ed margin. In fig. 4, which 



little further developed, the same three types of leaves are found. Pigs. 3 and 4 should 

 he compared with fig. 13, PL 2. figs. 14 and 16, which sh.ow that the O. ImvifoUa rosette 

 passes through the same series of developmental stages as 0. LamarcTciana. Indeed, 

 these three figures are. perhaps, indistinguishahle from figs. 3 and 4 of O. Lamarckiana 

 in photographs, yet the earlier stage (fig. 15) of 0. laevifolia is plainly different from the 

 corresponding stage of O. LamarcTciana (fig. 1). !From such facts one learns that types 

 which are at first divergent may converge during development, and later diverge again 

 so that the adults are as unlike as the young seedlings. In Oenothera^ as the plants 

 grow, such changes are constantly going on, and they add much to the complexity of the 

 facts, and greatly increase the necessity for the most detailed observation and comparison 

 of the individual plants in all the stages of their ontogeny. The necessity for this 

 becomes particularly strong in dealing with hybrids. 



After the third type of rosette-leaf appears there follows a continuous succession of 

 leaves of this type, the leaves of each cycle being longer than those of the preceding 

 cycles (though otherwise the same), until a maximum diameter of the rosette is reached 

 (PI. 1. fig. 5). After this, if the rosettes of 0. Lamarckiana or its derivatives are kept 

 under constant conditions of high temperature and high moisture content, leaves of the 

 same type continue to appear, the older ones dying away below, until a considerable 

 area of stem may be formed without internodes (see Gates, 1912). The plants will 

 usually continue to produce rosette-leaves as long as these tropical conditions are 

 prolonged. Under ordinary conditions of culture, however (in which, the seeds are sowti 

 in pans in January, the seedlings afterwards transplanted to pans in the greenhouse, and 

 the young rosettes planted out-of-doors in May), a stem soon begins to form. The lower 

 cauline leaves form a somewhat abrupt transition from the rosette-leaves. As observable 

 from figs. 7 and 8, the upper stem-leaves are sessile or nearly so, with a broad, more or 

 less aurate base, and they diminish gradually but strongly in length and width in 

 passing up the stem. The lowermost stem-leaves have long petioles and elongated 

 blades like the rosette-leaves, but these quickly change above to the cauline type of leaf 

 having a very short petiole and shorter, aurate blade. The leaves of the whole organism 

 therefore form a continuous series, whose continuity is, however, broken by rather sharp 

 transitions at two places in the rosette development, and also in the passage from radical 

 to cauline leaves. In Oenotheras of the Lamarckiana group there is, under the 

 conditions of my cultures, a considerable pause after the maximum diameter of the 

 rosette is reached, during which further cycles of rosette-leaves of the same type 

 continue to be produced, before elongation of the stem begins. 



In PI. 1. fig. 6 are shown six leaves selected from typical mature rosettes of 

 O. Lamarckiana at this time, to show the range of variation in the length, width, and 

 poiutedness of the leaves at this stage. With this should be compared PL 2. tigs. 18 and 

 23, selected respectively from 0. laevifolia and 0. brevistylis to show their ranges of 

 variability in the same stage of development. It will be seen that if the leaves of all 



