The leaf sheaths of certain wheat plants and one variety of oats that are resistant to hessian fly attack appear to have a much more complete and even distribution of silica deposits on their surface than do those of susceptible varieties. The silica deposits in the latter varieties are in the form of rod-shaped masses which are arranged in dispersed rows. The density of deposition depends on the physiological age of the plant. and emphasizes the necessity of considering this factor in studying the problem of resistance. Certain varieties were demonstrated to have silieified hairs on the surface of the sheath. Most of these varieties were susceptible to hessian fly attack. These results suggest that the presence of silica depositions on wheat plant tissue may be one of the factors related to resistance of certain varieties to hessian fly attack. Since there are several parental sources of resistance to hessian fly other factors also may be involved.
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Miller et al. (1960) studied this question.