ANALOGY OF PLANT ORGANS. 59 



On the otlicr hand, stems; often resemble leaves not onlv in form, 

 but also in constitution and function, as in the folluwiug examples: — 



(1) Thick, stem-like, but green, and bearing no leaves, Cactus, Ei<phorbia. 

 ('2) Foliaoeous, but fleshy, Epiphi/llum, which closely resembles the leaf of 

 Bnjophylliiin. 



(3) Acieular, as the " cladodia " of Asparagus, which nearly resembles the 

 segments of the leaves of Raiuittculiis aijuulUis and fennel, etc. 



(4) Flat, and more or less herhaccous in texture, the •' phyllocladia " of Euscus, 

 Xylophylla, and the stems of some leguminous plants. 



These plants possessing no true leaves, the assimilative properties 

 are therefore entii'cly sustained by the stem-structures themselves. 



IV. Axial Structures — Reproductive. 



Before discussing the homologies and metamorphoses of the floral 

 wborls, the changes undergone by the floral axes need to be 

 alluded to. Commencing with the normal condition, the various 

 departures fi'om it may be classified as follows : — 



i . Normal, that is exhibiting no special difference in development, 

 appearance, or function from ordinary stem-structures. 



2. Cirrhose, as in the vine and Virginia creeper, of which Mr. 

 Darwin has described the tendrils as homologous with flowering 

 branches.* 



3. Culorised, as in JTijacinflmn comosa, var. monstrosa. In this 

 species there is a gradual degeneration of the flowers, the stamens 

 and pistils becoming more and more atrophied, while the perianth 

 dwarfs until the entii'e flower vanishes altogether, nothing remaining 

 but tufts of coloured pedicels borne by a similarly coloured peduncle 

 with bracts scattered over the surface. f The brilliantly coloured 

 fasciate stem of the garden cockscomb is another instance. Coloured 

 pedicels are far fi'om uncommon. 



4. Hook elinihers. A good illustration is seen in Uncinia, in which 

 the peduncle ciuis into a hook after flowering. 



5. Burroioing apparatus. This is seen in the rigid sharp-pointed 

 apex of the peduncle of Trifuhiwi subterra)ieu)n, which buries its 

 fruiting head beneath the soil. 



6. Reservoirs of nutriment for the fruit and seeds. The receptacles 

 of Compositce, as of the artichoke, the appendix to the spadix of 

 Aroids,;]: the pseudocai-p of the strawberry, cashew, and rose, as well 

 as the inferior pome of the tribe Pomece, of the order Rosacea. 



7. Attractive. The coloui'cd inferior berries and pomes of many 

 plants. 



8. Abnormal modifications of axial structure occur as fasciated 

 stems; e.g. cockscomb ; pear-shaped axes of vegetative buds of Pyrus; 

 pedicellate flowers of barren orchids, resembling the pedicel (normal) 

 of the ray flowers of Centaurea, and the hypertrophy and colorisation 

 of the axes of Hyacinthus comosa, var. monstrosa, described above. 



* ' Climbing Plants,' p. 137. 



t ' Bulletins de I'Acad. Royale de Belgique,' tom. xvii, part 2, p. 29. 



J I have found that of Arum maculatum to have its cells laden with starch. 



