The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . icuin,which, being an annual, seemed more suitable. In thespring of 1892 I selected a single hemi-tricotylous seed-ling found in a sowing of commercial seed (a little lessthan 20,000 seedlings), and from this bred a race wdiichin the first year exhibited nothing remarkable but pro-duced fasciations in the second year and traces of twist-ing in the third, and finally, in the fourth, some veryfine instances of spiral torsion. One of these had thewhole main stem transformed into a screw (Fig. 74)
The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . icuin,which, being an annual, seemed more suitable. In thespring of 1892 I selected a single hemi-tricotylous seed-ling found in a sowing of commercial seed (a little lessthan 20,000 seedlings), and from this bred a race wdiichin the first year exhibited nothing remarkable but pro-duced fasciations in the second year and traces of twist-ing in the third, and finally, in the fourth, some veryfine instances of spiral torsion. One of these had thewhole main stem transformed into a screw (Fig. 74).Fortunately in such experiments, the aim can be attained,as a rule, in a much smaller number of years. ^Monographic dcr Zzcan^sdyeJiun^cu. Prixcsheims Jahrb. Bot., Vol. XXIII, p. ii6. Bull. Acad. Roy. BcJg., Vol. XVIII, p. zy. Tricotyiy and the Arrangement of Leaves. 369 Tricotylous s|)cciincns of species willi ;i decussatearrangement of their leaxes very often produce tlie lowerleaves of the stem in whorls of three. Sometimes thisextends all the way up, or at least to the inflorescence,. Fig. 74. Dracocephahim moldaviciun. Twisting of themain stem as the result of a breeding experiment ex-tending over four years. (Compare below Fig. 82.) sometimes, however, it reverts to the decussate arrancre-ment sooner or later as we proceed ui)wards. Very oftenalso the latter follows immediately on the seed-leaves(Fig. 76 B). All such cases can often be observed in J/ 0 Tricotxious Races. the same culture from the seeds of a single is especially the case in Anfirrliiniiin iiiajiis andScropJiularia nodosa, in which species I have often pre-ferred as seed-parents, the tricotyls, whose first whorlswere trimerous. Nevertheless they have not, as a rule,proved the better qualified to continue the character oftlie race. Further instances are afforded by Dipsaciissylvestris, Lychnis fidgcns, Dracoccphaluin nioldavicunu Dianthus harbafus and soon. Tn the spring of 1887 Tha
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