One hundred years is a pretty short time frame when you start asking for differences between two groupings of plant types. In that time frame, there probably haven't been many significant developments. Both of these are flowering plants, the difference seems to lie in their parts and pieces. Monocots have one cotyledon leaf, which contains the energy needed to get the seedling plant going, while dicots, have two cotyledon leaves. Monocots tend to have their leaves with parallel concentric circles, while dicotyledons tend to have a vascular network of veins in their leaves. The flowers of moncots tend to have groupings of three, while the flowers of dicots tend to have numbers of four to five. The seed of a moncot is all together in one piece, while the seed of a dicot is easily split apart into two equal pieces. A good example of a monocot is corn, while a good example of a dicot is a lima bean. There are many other differences that can be pointed out between the two, but evolutionary developments within a hundred years is not enough time to clearly outline developmental differences.