COMPARISON OF TRICHOMES IN PURE SPECIES AND HYBRIDS. 61 



CONCLUSIONS AND RESULTS. 



The 11 different species and the hybrids derived from them, which were 

 employed in the course of the investigation, represent an interesting range 

 of habits and life conditions as well as types of variation and reversion. 



The pure species are both arborescent {.Juglans) and herbaceous. The 

 herbaceous plants are annuals {Papaver somniferum, So/an urn villosum), 

 biennials {Oenothera lamarckiana, Oenothera cruciata), or perennials {So/a- 

 na in guinense, Papaver orientate, Papaver pilosum) . 



The feature of fertility or sterility of the hybrids is as follows: Those 

 wholly fertile are Solatium villosum. X Solanum guinense (5 generations 

 have been observed); Oenothera lamarckiana X Oenothera cruciata (3 and 

 more g-enerations have been studied with regard to this characteristic); 

 Juglans calif ornica < Juglans nigra. The wholly sterile hybrids are Papaver 

 somniferum X orientate. Juglans californica < Juglans regia and Papaver 

 somniferum are partly fertile. 



Several types of reversion are known among the hybrids, so far as this 

 feature has received particular study, and further observation would prob- 

 ably reveal still other reversion characteristics. 



Two hybrids, Oenothera lamarckiana < Oenothera cruciata* and So lanum 

 guinense X Solan um villosum, are fixed forms in the first as well as the 

 succeeding generations, so far as observed. In the Oenothera hybrid 

 there is a mingling of the parental characters, no new character appearing, 

 but the Solanum hybrid exhibits, in the fruit, a condition not found in 

 either pure parental species. The Papaver and the Juglans hybrids, first 

 generation, are extremely variable as regards the leaf-characters. The 

 type of reversion in Juglans hybrids, of the second and third generations, 

 has not been closely studied, but may be Mendelian. The Mendelian 

 characteristic of dominance w r as not observed in any hybrid . 



Two general forms of trichomes were seen in nearly all of the hybrids 

 and the pure species living forms (which are glandular) and non-living 

 forms. After some study it was learned that the living forms of trichomes 

 had more of interest for the subject in hand, so that for the most part this 

 paper reports the behavior of such trichomes. In the Oenotheras the 

 glandular trichomes are unicellular, but in the other species they are mul- 

 ticellular, and in certain of them, particularly in Juglans, the develop- 

 ment of the trichomes was followed and was found of value for comparative 

 purposes . 



As repeatedly observed during the course of the study, the trichomes 

 were found to present considerable range in size, which is meant to apply 

 to any type, and this was found to be the case both in pure lines and in 

 hybrids. The extremes in variability were no more marked in the latter 



*Mutations, Variations, and Relationships of the Oenotheras, by MacDougal, Vail, 

 and Shull. Carnegie Institution of Washington Publication No. 8i, 1907. 



