THE NATURE OF THE FLESHY SHOOT OF ALLENROLFEA AND ALLIED GENERA

JAMES, Lois E. (Whittier Coll., Wlhittier, Calif.), and DONALD W. KYHOS. The nature of the fleshy shoot of Allenrolfea and allied genera. Amer. Jour. Bot. 48(2): 101-108. Illus. 1961.-A number of genera of the Chenopodiaceae are characterized by what have been called fleshy internodes which make them appear jointed. The fleshy tissue comprises on the average the outer 2/3 of what superficially appears to be the stem. This fleshy tissue contains a vascular network which is continuous with and similar to the vascular network in what has commonly been called the scalelike leaf. The problem is whether this fleshy vascularized tissue is the result of a downward prolongation of the base of the leaf or whether it is actually the true cortex of the stem. The present authors have found that Allenrolfea is uniquely suited to solving the problem of the so-called fleshy internodes of these allied genera. The origin and development of the fleshy tissue indicate it to be foliar. This conclusion is further substantiated by the shape of the fleshy tissue, its phyllotactic arrangement, the extent of the palisade tissue and underlying vascular network, the pattern of branching of the leaf traces, and the effect of secondary thickening and suberization. MEMBERS of the Chenopodiaceae are character3tically found in saline or alkaline soils and are rorldwide in distribution. Many of the members re found only on the deserts and others only in salt marshes. A few, such as beets, chard, and spinach, are cultivated. Members of one intriguing group of Chenopodiaceae have fleshy and jointed stems. Salicornia L., Halocnemum Bieb., Anabasis L., and Allenrolfea Kuntze are genera included in this group. In these plants, what appears to be stem is comparatively large and succulent except just above a node where the diameter is commonly reduced to about 1/3 that of the fleshy part. This gives the stem a sort of "linked-sausage" appearance. All that one sees of a leaf is a small scale-like protuberance. These scale-like protuberances are alternate in Allenrolfea (fig. 1) although in most of the genera they are opposite. Some of the early botanists (De Bary, 1884; Ganong, 1903; Cross, 1909) considered these plants leafless, but, more recently, taxonomists have considered the protrusions as leaves (Jepson, 1923; Peck, 1941; Abrams, 1944; Munz, 1959). The chief reason this unique type of plant has attracted the attention of a number of investigators is that a vascular network occurs in the fleshy joint below each scale-like protuberance. It is the question of the origin or significance of this fleshy vascularized tissue that has again become a matter of consideration. The fleshy tissue consists of epidermis, palisade parenchyma, vascular network, and an inner layer of large, thin-walled cells that look like spongy parenchyma (fig. 8, 9). This layer has been referred 1 Received for publication January 14, 1960. The work of the senior author was supported in part by a grant from the Danforth Foundation. to as water storage tissue (Halket, 1928; Metcalfe and Chalke, 1950; Fahn and Arzee, 1959). Internal to this is what would appear to be the unmodified cortex and stele of the true stem (fig. 7, 11). The upper boundary of the fleshy mass is continuous with the leaf protuberance, but the extent of the lower boundary depends upon the age of the stem. In young stems, the fleshy mass reaches almost to the node below (fig. 4), but in older stems elongation has occurred in the lower part of the internode, and this part of the stem will be free of fleshy tissue. Most previous workers (Duval-Jouve, 1868; Dangeard, 1887; Cooke, 1911; De Fraine, 1912; Halket, 1928; Leysle, 1949) are in agreement that this outer fleshy tissue is foliar in origin. Fahn and Arzee (1959) have concluded otherwise and maintain that the fleshy tissue and its vascular network are cortical in origin. The work of Fahn and Arzee (1959), as well as that of earlier investi. gators, has been done on members of the group with opposite leaves. The present investigators believe that Allenrolfea provides convincing evidence of the foliar origin of the fleshy tissue. It is the presence of alternate, instead of opposite, leaves that makes Allenrolfea especially suitable for an interpretation of the succulent tissue of the jointedstemmed members of the Chenopodiaceae. For clarity, the fleshy tissue around the stem will be referred to as leaf base or outer cortex and the term true stem will be used to refer to the stem without the attached leaf base. The following will be considered: (1) an account of the characteristics of Allenrolfea that are pertinent to an interpretation of its stem and leaf structure; (2) a comparison of Allenrolfea with other fleshy Chenopodiaceae; (3) an interpretation, in [The JOURNAL for January (48: 1-100) was issued January 23, 1961] AMERICAN JOURNAL OF BOTANY, Vol. 48, No. 2, February, 1961