The observer is sometimes embarrassed in deciding to which whorl he should refer the foliola he is examining. Thus, the tiny foliola which, in the strawberry and the potentilla, alternate with others and larger ones, are stipules rather than sepals. Ought the sepals of the calyx in the Malvaceæ to be assimilated in like manner to the stipules? It is difficult to reply to this question satisfactorily. Take, for example, the _Hibiscus Syriacus_, an ornamental shrub, better known by the name of the garden-hemp. The inner calyx, or calyx properly so called, of this Malvacea has five sepals, while the outer calyx, or calicule, has twelve. Now, a leaf cannot have more than two stipules, one on each side. For an outer calyx, then, the proper number of foliola is ten, not twelve. To look upon the second calyx as a "supernumerary development," would be to hazard a supposition contrary to the unity of plan of the floral organs. * * * * * The calyx, like the corolla, is not an absolutely indispensable organ. Sometimes, therefore, it is _caducous_--that is, falls off before the flower expands,--as in poppies; sometimes, _persistent_, or remains after flowering,--as in roses and the majority of plants. In some cases it is persistent only until after the act of fecundation, but this act accomplished, it falls with the corolla in most of the Cruciferæ and Ranunculaceæ. This is a _deciduous_ calyx. The "caducity" and "persistency" of floral envelopes furnish some valuable characteristics for the distinction of species. Thus, two closely-allied Cruciferæ, the _Alyssum calicinum_, so common in spring upon stony soils, and the _Alyssum montanum_, can only be distinguished from one another by the fact that the calyx of the former is persistent, of the latter caducous. It is true that the flowers of the _Alyssum calicinum_ are of a yellow which easily passes into white, while those of the _Alyssum montanum_ are of a beautiful permanent yellow. But this latter distinction is not so good as the former. The persistent calyx sometimes assumes a considerable increase of very common appearance. For example, take the _Physalis alkekengi_, a member of the Nightshade family or Solanaceæ. The red bladder-like accrescence surrounding the scarlet fruit is the calyx, which, after flowering, has grown much larger than it was before. And these bright flowers which resemble large strawberries, and abound on the borders of meadow-paths, if you look at them closely, you find to be the accrescent calices of the _Trifolium fragiferum_. The very word _fragiferum_ reminds us of the strawberry.