In _Cephalotus follicularis_ rudimentary or imperfect pitchers may be frequently met with, in which the stalk of the leaf is tubular and bears at its extremity a very small rudimentary leaf-blade. It is not in all cases easy to trace the origin and true nature of the ascidium, as the venation is sometimes obscure. If there be a single well-marked midrib the probability is that the case is one of cohesion of the margins of the leaf; but if the veins are all of about equal size, and radiate from a common stalk, the pouch-like formation is probably due to dilatation and hollowing of the petiole. Again, when the result of a union of the margins of the leaf, the pitcher is generally less regular than when formed from the hollowed end of a leaf-stalk. Further information is especially needed as to the mode of development and formation of these tubular organs, so as to ascertain clearly when they are the result of a true cupping process, and when of cohesion of the margins of one or more leaves. (See Cohesion, p. 31. For bibliographical references consult also A. Braun, 'Flora v. Bot. Zeit.,' 1835, t. xviii, p. 41, _Aristolochia_.) =Tubular formations in the flower.=--A similar formation of tubes happens in some double flowers; for instance, it is not infrequent in double flowers of _Primula sinensis_, in which tubular petal-like structures are attached to the inner surface of the corolla; sometimes these petaloid tubes replace the stamens, while at other times they appear to have no relation to those organs. In the particular flowers now alluded to the tubular form seems due to a dilatation, and not to a cohesion of the margins. (See Cohesion, p. 23.) These tubular petals resemble in form and colour almost precisely the normal corolla in miniature, but are not surrounded by a calyx, nor do they contain stamens, while the less perfect forms show clearly their origin from a single tube-like organ. [Illustration: FIG. 168.--Corolla of _Primula sinensis_ turned back to show a tubular petal springing from it. One only is shown for the sake of clearness; they are generally numerous.] The formation of spurs or spur-like tubes in a quasi-regular manner has been spoken of under the head of Irregular Peloria, p. 228, but we occasionally meet with tubular processes which seem to occur in an irregular manner, and to have no reference to the symmetrical plan of the flower, and which are due probably to the same causes as those which induce hypertrophy. Such spurs have frequently been seen on the corolla of _Digitalis purpurea_, _Antirrhinum majus_,[352] _Tulipa Gesneriana_, and occasionally on the sepals of _Fuchsia_. They are very frequent in some seasons in the corolla of certain calceolarias (_C. floribunda_). By Morren this production of adventitious spurs was called "Ceratomanie." [Illustration: FIG. 169.--Corolla of _Calceolaria_, showing irregular tubular spurs projecting from the lower lip.]