In 1910[10] Tower published an account of further experiments with Leptinotarsa. The work described related to two subjects. Crosses were made between three forms, undecimlineata Stål, signaticollis Stål and "diversa" named by Tower as a new species. The distinctions between these three depend partly on characters of the adults and partly on those of the larvae. The adults of undecimlineata and diversa have the elytra striped, but the elytra of signaticollis are unstriped. The larvae of signaticollis and of diversa are yellow, but those of undecimlineata are white.[11] Moreover, in signaticollis and diversa the black increases in the third stage of the larvae to form transverse bands which are absent in undecimlineata. The general course of the experiments shows that these differences may be approximately represented as due to the action of three factors, any of which may be independently present or absent. The stripings of the elytra and of the larvae are each due to a separate factor. As regards the distinction between the yellow and the white larvae the evidence does not prove that there is decided dominance of either colour and I infer that the heterozygotes are often intermediate.
The chief contribution which this new paper claims to make relates to differences in the results which ensue from crosses effected between these three types at different average temperatures.
We are first concerned with four experiments which I number (1), (2), (3), (4):
1. Signaticollis ♀ × diversa ♂ bred at an average temperature of 80º F. by day and 75° F. by night, gave two groups in about equal numbers. The first (49) was pure signaticollis and bred true. The second (53) was of an intermediate type, which on being bred together gave the typical Mendelian result—1 sig.: 2 intermediate: 1 div.
2. Next, as the account originally stood in the published paper, we are told that sig ♀ × div ♂ bred together at a day-temp. average 75° F. and night average 50° F. gave an intermediate only, which subsequently produced a normal 1:2:1 ratio. The two crosses were repeated eleven times with identical results.
In a further experiment (3) signaticollis ♀ × diversa ♂ were bred under the same conditions as those used in expt. (1). They again gave sig. and intermediates as before in fairly equal numbers. The sig. as before bred true, and the intermediate gave 1:2:1, all exactly as in expt. (1).
In expt. (4) the same parents used in (3) were again mated under conditions of expt. (2) at the lower temperature, and this time gave signaticollis exclusively, which bred true for four generations. This experiment was repeated seven times with uniform results.
Diagrams are given representing all these histories in graphic fashion.
From these observations, Tower concludes that the determination of dominance, and the ensuing type of behaviour, is clearly a function of the conditions incident upon the combining germ plasms.
It will be observed that expts. (1) and (3) gave identical results but (2) and (4), though much the same conditions were applied, are at variance, for (2) gave all intermediates, while (4) gave all signaticollis. In Amer. Nat., XLIV, 1910, p. 747, Professor T. D. A. Cockerell commented on this paper of Tower's and pointed out that there must be an error somewhere, for when he discusses these experiments Tower speaks of (2) and (4) as confirming each other. To this Tower replied[12] that there had been a mistake. He states that in preparing the paper "certain minor experiments were taken from a larger series and combined to illustrate a general point in the behaviour of alternative characters in inheritance," and that expt. (2) was introduced inadvertently in place of another which he desires to substitute. In this, which I number (5), signaticollis ♀ × diversa ♂ from exactly the same stocks as those used in (1), were mated at the lower temperatures specified for (2), day average 75° F., night average 50° F. These gave all of the signaticollis type with a narrow range of variability, which bred true, in some cases to F6. Tower says he has repeated this experiment six times with identical results.