The Bearing of Teratological Development in Nicotiana on Theories of Heredity

Abstract

IT is desirable, though difficult, to atack genetic problems by both pedigree-culture and cytological methods. It is desirable because the problems are viewed from different standpoints; it is difficult because few forms are especially favorable for either kind of work. The present paper is a preliminary report upon certain characters in a species fairly desirable from each point of attack.Among plants teratological phenomena are common, especially those known as fasciations, Masters2 citing, in 1869, 120 genera in which they were not infrequent.The term fasciation is a broad one and includes, from a genetic standpoint, some very different phenomena. At least two distinct kinds of variation are now emphasized in genetic work, somatic and germinal, although often it is impossible to distinguish between them except by experimental cultures. Fasciation is a phenomenon of variation in which both types occur, though the evidence on this point is not all that could be desired. All observers agree that the fasciated character is constant and heritable in such races as Celosia cristata3 (cockscomb), Pisurn, sativumn umbellatum,4 Sedum refiexiun cristata,5 some races of Zea mays and Nicotiana No. 556] DEVELOPMENT IN NICOTIANA 207 tabacumn fasciata. On the other hand, many examples of fasciation are slight or severe somatic modifications, no more permanent than a swollen limb due to a bruise in our own bodies, or a bone spavin in a horse's foot, though the tissue proliferation may remain as a lasting scar. Examples of this form may be found in (Enotherc.7 Nasturtium,8 Picris hieracioides and Raphanus raphanistrum Y11.9 Such modifications are imperfectly understood, but may be brought about directly or indirectly by external agencies such as bruises, culture methods and insect injuries to the initial meristem. Aside from the work of Mendell" and De Vries," the phenomena of fasciation have not been dealt with in the liRht of modern genetics. Mendel's investigations were made on a fasciated strain of pea (Pisumn sativutm -um bellatum,),). When crossed with a non-fasciated strain the teratological character was recessive and segregated in F. in a simple 3 :1 ratio. This result -was essentially confirmed by Lock and Bateson, although environmental conditions were found by them to affect the character more than is usual in such phenomena. De Vries failed to distinguish between fasciations strictly heritable and those non-heritable. The only con-Exp. Stc. Bilt., No. 167, and Contrlib. from Lal. of Genetics, Bussey Inst. of Harvard Univ., No. 9, p. 133, P1. XXII (a) aud (b), 1911; also Emerson, R. A., personal communication, 1911. TK nox, A. A., ''Inlduetion, Development and Heritability of Fasciations,'' Carnegie Inst. of Wash. Pub. 98: 1-21, Pls. I-V, 1908.

Studies of Teratological Phenomena in their Relation to Evolution and the Problems of Heredity

“…This is the plant structure most commonly altered by fasciation. The variation in form this takes has been adequately described in the preceding pages and in a former paper (White 1913).…”

“…The technical work was always personally looked after. The methods used in the cytological phase of this investigation are described in an earlier paper (White 1913).…”

“…These data are subject to tile criticism that in a study of environmental effect on plants, seed from the same, instead of from different plants, should be used. But this criticism is probably invalid here, because the fasciated race is a pure line upon which selection (White, 1913) same value whether from the same plant or generation or different plants in different generations. The tent-grown plants in Connecticut had a higher average number of leaves than the plants of the 1910 culture at the Bussey Institution.…”

“…In a former paper (White, 1913) the statement was made that the fasciated character of the 300--309 race did not seem any more amenable to selection than the race of cockscombs with which de Vries worked. In other words, from two generations of selection for normalness, no effect seemed to be apparent, so the attempt for the time, was given up.…”

“…The experimental results and data from this cross have been given in detail in an earlier paper (White, 1913). The F2 population contained abnormals (AA), intermediates (Aa), and normals (aa) in the proportion of 1:2:1.…”