## 4 Discussion
### Biological Application  
Plant structure and physiology change over time; therefore, timing of trait measurements is important. Although growth on a gross spatial-temporal scale appears to be linear and equal across all dimensions, this is not always the case. Cell division only occurs at meristems, and in the case of cereals only at the apical meristem. Cell division also occurs only when cell expansion in a region has reached a specific point [27]. On a macro level cereals plants expand outward (i.e., tiller) before initiation of elongation (i.e., increase in height). This pattern of growth repeats over the life span of the plant. Wheninjury occurs the plant resources can be transported to the injury location and regenerative growth occurs (i.e., callus or scar tissue) [28].  
Weather events might also impact timing of a trait measurement, for example plants grown in high soil moisture have higher water potential [29] which is known to impact the mechanical properties [30]. In this study, stem maturity was found to impact stem strength and change in power of the stems as they were bending and unbending. To quantify the most traits during one measurement, the optimum timing for deployment of this machine is at or right before grain maturity and before senescence.  
Push force has already been investigated and used in determining lodging resistance potential of wheat for management [8] and breeding decisions [7]. Stem strength could be used as an individual proxy lodging trait for oat breeding [11] as it is in wheat [7; 8]. Furthermore, this technique has been incorporated into predictive lodging models [1; 31; 32]. Similar to previous studies, wheat classified as lodging susceptible in this experiment had a significant reduction in stem strength. Oat also expressed similar trends, where lodging susceptible lines exhibited less push-force.  
Some of the measured components of elasticity could differentiate between lodging resistance and susceptibility depending on the cereal type. In oat, initial displacement differentiated between lodging classifications, whereas the change in energy and power required to bend and unbend a stem differentiated lodging classification of barley and wheat. These differences in classification are most likely linked to the minute differences between the internal structures of the grass species [33; 34] and not material properties [35]. The arrangement of internal structures within the stem are more important than their individual material properties [36; 37] because the arrangement does not change after initial deformation, unlike material properties [33].  
Both stem strength and components of elasticity could allow breeders to make selections within breeding material to increase genetic gain for lodging resistance without waiting for storm events or inducing lodging with expensive environmental equipment. These traits have not been used in plant research for lodging selection as of yet. Although our observations from a small number of genotypes provides some new insight, exploring a larger and more genetically diverse collection of genotypes would yield a better understanding of heritability and genetic architecture underlying these traits. The development of a selection index that combines stalk strength, displacement, and change in power would take into account both strength and elasticity of a stem and could be used to replace the current rating scale. However, this type index also needs to be investigated with a larger genetic pool.