The following traits of pea plants selected by Mendel, were not observed by him in ${\mathrm{F}}_1$generation of his monohybrid crosses.

I. Dwarf plant 

II. Wrinkled seeds 

III. Axillary flowers  

IV. Violet flowers

Dwarf plant height is recessive to tall heighted pea plant. Wrinkled seeds are recessive to round seeds. Hence these traits were not observed by Mendel in the off spring of parents. Axillary flowers and violet flowers are dominant traits and they are observed in offspring of respective parents.