2:07 AM, Sunday July 11th 2021
RE: Potato plant
Yeah I can see why you did it, but black areas in this course should be exclusively cast shadows. In the demo it is done as a cast shadow, with all the leaves above that area basically causing the entire area to be black. However, if you want to capture that cast shadow, you must capture all of the cast shadows in the composition.
RE: Cactus
I was mainly basing this on the demo where there was a pretty pronounced dish-like shape to them. Looking at more examples, I definitely see what you mean though. I guess that's just the nature of that particular plant.
RE: Trees
Remember that the purpose of this lesson is not to learn how to draw plants, but rather specific ways of construction that apply well to leaves and branches. Trees have way too many of both to construct them one by one, and therefore none of the construction techniques apply to them. You have constructed them well, but they don't really apply the principles of the lesson.