INTRODUCTION. 



21 



sibilities of the breeder than those of Burbank. In re- 

 ferring to the results obtained by crossing and selection 

 in general, he states ( New Creations of Plant Life, Har- 

 wood, 1912, 216) that "there is no barrier to obtaining 

 fruits of any size, form, or flavor desire'd, and none to 

 producing plants and flowers of any form, color, or fra- 

 grance. All that is needed is a knowledge to guide our 

 efforts in the right direction, undeviating patience, and 

 cultivated eyes to detect variations in values." 



If starch characters are heritable they should, in 

 order to meet theoretic requirements, exhibit peculiari- 

 ties of inheritance corresponding to those observed in 

 gross and microscopic anatomic plant characters. This 

 deduction will be found to have ample justification in the 

 results of this research. Herein it will be found that the 

 starches of the hybrids frequently exhibit in histologic, 

 polariscopic, and physico-chemic properties some degree 

 of intermediateness between the parents, usually nearer 

 one or the other. In any given hybrid certain of the 

 properties may be exactly or practically exactly inter- 

 mediate, and other properties may be identical with the 

 corresponding properties of one or the other parent. In 

 many instances one or more of the characters of the 

 hybrid, such as the relative number and the types of 

 compound grains, the degree of fissuration, the regu- 

 larity or iregularity of the forms of the grains, the 

 characters of the hilum, the distinctness and size of the 

 lamella?, the polariscopic properties, the temperature of 

 gelatinization, the aniline reactions, and the qualitative 

 and quantitative reactions with the various chemical reag- 

 ents, were developed or manifested in degrees beyond 

 the parental extremes. Moreover, peculiarities of various 

 kinds were observed at times in the hybrid that were not 

 apparent in either parent. In so far as these results go 

 they are, in general, in entire accord with the experience 

 of the plant and animal breeder and with unquestionable 

 statements of literature. 



The doctrine of intermediateness of the microscopic 

 characters as set forth in a preceding section is not war- 

 ranted by the literature of naked-eye characters and 

 is opposed to the results of the work with starches. This 

 led to supplementary studies of the macroscopic and 

 microscopic characters of parent- and hybrid-stocks 

 which compose Chapter IX of Part II. It seems clear 

 upon general grounds that if characters of the starch of 

 the hybrid may be intermediate, dominant, recessive, 

 blended, modified, developed beyond the parental ex- 

 tremes, new characters developed, etc., corresponding 

 phenomena should be exhibited by the tissues. It was 

 expected when this part of the research was planned that 

 in the case of each plant both starch and tissues could 

 be studied coincidently and compared, but this was found 

 to be impracticable; therefore the studies of the plant 

 tissues were carried on as an independent but correlated 

 research. Here, as with the starches, excepting Ipomcea, 

 the specimens of both parent- and hybrid-stocks are of 

 the first generation that has been perpetuated from year 

 to year by the propagation of tubers, pseudo-tubers, rhi- 

 zomes, bulbs, bulbils, etc. Both of the parent- and the 



hybrid-stocks of Ipomcea were grown from seeds which 

 breed true. The hybrid is of the offspring of successive 

 annual seed plantings since 1908, and probably represents 

 the sixth or seventh in the line of descent. The seeds 

 were obtained from the originator of the hybrid, and the 

 other stock from reliable plant-growers. 



The different specimens of starches were prepared 

 from a number (varying usually from 5 or 10 to 100 

 or more) of bulbs, rhizomes, etc., so that the prepara- 

 tions may be taken as representing a fair mean ; but with 

 the plants used for the supply of tissue we were dependent 

 in each case usually upon one or two specimens which 

 may be taken to be of about the average or fairly 

 representative. 



In selecting the material from the different plants 

 for the microscopic preparations the precautionary meas- 

 ures promulgated by Macfarlane (page 4) to secure safe 

 comparative results were as far as possible carefully 

 followed out. Inasmuch as there is a tendency for indi- 

 viduals of a species, even when grown under the same 

 conditions, to vary in one or more of their characters 

 from the average degree and manner of development, 

 macroscopically and microscopically, it is manifest that 

 in a comparative examination of parents and offspring 

 there should be studied either the actual parents and a 

 selected typical specimen of the hybrid that exhibits the 

 average mean properties of the hybrids, or typical speci- 

 mens of both parent- and hybrid-stocks. When neither 

 is practicable, as was the case in the present inquiry, 

 there are probabilities that the relative values of the 

 various characters may not be wholly correct, as for in- 

 stance, a given character of the hybrid may be inter- 

 mediate but nearer one or the other parent instead of 

 being exactly mid-intermediate, or vice versa, as might 

 be the case had the plants been very carefully selected 

 upon the basis of the specificity of intermediateness. 

 On the other hand, it goes without saying that in the 

 selection of the hybrid the assumption that the one hav- 

 ing most nearly properties that are exactly intermediate 

 between those of the parents is a typical hybrid is certain 

 to lead to the worst of pitfalls, because it of necessity 

 implies that blended inheritance is a sine qua non; there- 

 fore, as a corollary, that having a given hybrid its 

 parentage might positively be detected by the selection 

 of species that have characteristics such as would meet 

 the theoretical requirements of intermediateness in the 

 hybrid. It is obvious that such a plant might be far 

 more undesirable and even absolutely unreliable for com- 

 parative purposes than one that has the least degree of 

 intermediateness, because the latter but not the former 

 may typify the mean of the hybrid characteristics. The 

 results of various investigations fully justify the state- 

 ment that intermediateness may be absolutely misleading 

 as a criterion in the recognition of hybrids. 



8. UNIT-CHARACTERS AND UNIT-CHARACTER- 

 PHASES. 



The term character is used throughout this research 

 in a conventional sense to signify any property that 



