In all these cases the bracts behave as with the Erucastrum, being limited to the base of the spike, and decreasing in size from the lower flowers upward. Connected with these atavistic bracts is a feature of minor importance, which however, by its almost universal accompaniment of the bracts, deserves our attention, as it is indicative of another latent character.

Besides the Sisymbrium some six other genera afford similar structures. Erucastrum pollichii has been already alluded to in a former lecture when dealing with the same problem from another point of view. As previously stated, it is one of the most manifest and most easily accessible examples of a latent character becoming active through systematic atavism.

But it is very interesting that this same cohesion is to be seen in the shepherd's purse, in the wormseed and in the cabbage, as well as in the case of the Erucastrum and most of the other observed cases of atavistic bracts.

Bracts in the inflorescence of crucifers are ordinarily wanting, but may be seen in some genera, Erucastrum pollichii being perhaps the most widely known instance, although other cases might easily be cited. For our special purpose we may take up only the more simple cases that may be available for experimental work.