STUDIES IN HEREDITY AS ILLUSTRATED BY THE TRICHOMES OF SPECIES 

 AND HYBRIDS OF JUGLANS, OENOTHERA, PAPAVER, AND SOLANUM. 



INTRODUCTION. 

 SCOPE AND PURPOSE OF THE STUDY. 



In investigating- the structural features of plants two or more methods 

 of approach, each especially adapted to the particular aim of the study, 

 whatever it may be, may be employed. The entire anatomy of a few forms 

 may be worked up, and appropriate comparisons instituted, or, on the other 

 hand, special features of the plant's structure, such as the trichomes, may 

 be minutely studied, both in the mature state and in embryonic condition, in 

 a relatively large number of individuals as well as great variety of species. 

 Although the former method has hitherto been the one chiefly employed 

 in anatomical studies on plant hybrids, it seems appropriate, in view of 

 the present tendency to regard a plant as a complex of more or less inde- 

 pendent units, to institute the more special study. Whatever theories may 

 be held, this manner of studying structures in plants, as in animals has 

 long been found, has several advantages. It permits, in the first place, 

 as suggested above, an examination into the behavior of the particular 

 organ, or tissue, in a much larger number of plants than might otherwise 

 be practicable, as, in the present instance, the trichomes of some 20 differ- 

 ent kinds of plants, and many more individuals, have been passed under 

 observation. It also favors an investigation into the variation of the par- 

 ticular structure, as well as into the relation of the variation to the organic 

 and the physical environment of the tissue as possible causal factors of 

 variation. Also, not only the mature structures, but the embryonic stages 

 likewise, may be studied and compared, so that developmental stages may 

 easily be contrasted, and, in favorable material, the possible origin of the 

 structures may either be traced, or at least strongly surmised. And, 

 finally, what is particularly important in a study on heredity, the behavior 

 of the same structure may be advantageously observed throughout differ- 

 ent generations. For these and other reasons the particular rather than 

 the more general method of the study of the anatomy of the hybrids has 

 been adopted in the present investigation. 



In selecting plant structures for comparative study, one or two points 

 were kept uppermost in mind. All of the plant tissues are not equally favor- 



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