Synopsis Evidence was presented that genes for yield per se do not exist in barley. Hence yield is an artifact. If there are no genes per se for yield, there can be no dominance effects due to yield genes, or for that matter no over‐dominance of yield genes or heritability of yield. F1 vigor was shown to be due to epistasis. A large share of the F1 vigor in this experiment was shown to be fixable in a true breeding form.

Selection of a new cultivar usually requires the manipulation of quantitative characters, many of which are correlated. These correlations may be due either to genetic linkages or to physiological and developmental relations. The latter two categories are considered here. The need for an understanding of these relationships is obvious because they impose constraints on the form of a plant and are frequently barriers to improved yield. The approach is based on Sinnott's law which states, “The size of an organ is proportional to the size of the meristem from which it develops.” In an attempt to relate this law to correlation between traits and to predict the tightness of the association, a dichotomy was proposed between: 1) the allometry associated with organs arising from the same meristem and 2) the allometry associated with organs arising from different meristems. It was predicted that generally the correlations in the first category would be expected to be harder to manipulate, but some of the latter category could also be recalcitrant. Examples were given for both categories including one in barley, Hordeum vulgare L., of an increase in yield due to manipulation of correlated traits not arising from the same meristem. Two corollaries to Sinnott's law were proposed. 1) Plasticity is inversely proportional to ontogenetic proximity. Traits arising from the same meristem will tend to be harder to manipulate than those separated in space and time of origin. 2) Numbers and size of organs tend to have an inverse relationship. Examples are given in support of both corollaries.

Synopsis Number of panicles per unit area (X), average number of kernels per panicle (Y), and average kernel weight (Z) are interpreted as the edges of a rectangular parallelepiped with the yield (W) as volume. Five theorems are developed and proved, and used as a basis for defining a universal variety.

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T HE problem of lodging in small grains has already received considerable attention, and rightly so, as resistance to lodging is an important limiting factor in the yield of a small grain variety. Researchers have studied environmental, morphological, cytological, physical and chemical factors in an attempt to find the reasons for lodging. Environmental factors such as thickness of stand (8, 12), soil nutrients (8) and sunlight and temperature (12) have been investigated. Plant characteristics, such as amount of schle