In some cases pitchers are only built up of part of the leaf-blade. Such partial malformations obey a rule, that is common to them and to other foliar enations, viz.: that the side of the leaf from which they emerge, is always their outer side. The inner surface of these enations corresponds to the opposite side of the leaf, both in color and in anatomical structure. The last of the four rules above mentioned is [245] that of the homologous variability. It asserts that the same deviation may occur in different, but homologous parts of the same plant. We have already dealt with some instances, as the occurrence of the same pigment in the flowers and foliage, in the fruits and seeds of the same plant, as also illustrated by the loss of the red or blue tinge by flowers and berries. Other instances are afforded by the curious fact that the division of the leaves into numerous and small segments is repeated by the petals, as in the common celandine and some sorts of brambles. It would take too long to make a closer examination of the numerous cases which afford proof of these statements. Suffice it to say that everywhere the results of close inspection point to the general rule, that the failure of definite qualities both in species and in varieties must, in a great number of cases, be considered as only apparent. Hidden from view, occasionally reappearing, or only imperfectly concealed, the same character must be assumed to be present though latent. In the case of negative or retrogressive varieties it is the transition from the active into a dormant state to which is due the origin of the variety. Positive varieties on the contrary owe their origin to the presence of some character [246] in the species in the latent state, and to the occasional re-energizing thereof. Specific or varietal latency is not the same thing as the ordinary latency of characters that only await their period of activity, or the external influence which will awake them. They are permanently latent, and could well be designated by the word perlatent. They spring into activity only by some sudden leap, and then at once become independent of ordinary external stimulation. [247] LECTURE IX CROSSES OF SPECIES AND VARIETIES In the foregoing lectures I have tried to show that there is a real difference between elementary species and varieties. The first are of equal rank, and together constitute the collective or systematic species. The latter are usually derived from real and still existing types. Elementary species are in a sense independent of each other, while varieties are of a derivative nature.