MORPHOLOGY OF MARSILEA VESTITA. I. ONTOGENY AND MORPHOLOGY OF THE SUBMERGED AND LAND FORMS OF THE JUVENILE LEAVES

During their ontogeny, the primordia of the juvenile leaves of Marsilea plants in sterile culture develop 1, 2 or 4 marginal meristems, and these, in turn, contribute cells to the young leaf by anti- and periclinal cell divisions. The final leaves are unifid, bifid, or quadrifid, depending on how many marginal meristems develop, and this is determined early in the ontogeny of the leaf. The mechanism which determines whether or not a marginal meristem develops may fluctuate, as shown by the existence of trifid leaves. Two forms of juvenile leaves are produced, those in a liquid medium, which in many respects resemble the adult quadrifid submerged leaves, and those on a solid medium, which in many respects resemble the adult land leaves.     

SOME ABNORMAL FLOWERS OF ARGEMONE MEXICANA AND THEIR BEARING ON THE MORPHOLOGY OF THE GYNOECIUM OF PAPAVERACEAE

Abnormal flowers of Argemone mexicana are described in whichthe gynoecium has been transformed into a cup with lobed marginor into free leafy carpels. The number of lobes or leafy carpelsin such gynoecia is found to vary from three to five. This agreeswith the general view of systematists regarding the number ofcarpels composing the gynoecium in this species, and is againstthe views of Saunders and Dickson who postulate twice as manycarpels.     

DEVELOPMENTAL MORPHOLOGY OF COTTON FLOWERS AND SEED AS SEEN WITH THE SCANNING ELECTRON MICROSCOPE

This report assembles and pictorially presents observations on the timing of relatively uniform and well-defined developmental events in the cotton flower and its component parts. The first floral bud occurs on the 7–9th node approximately 35–40 days postemergence; 20–25 additional days elapse until anthesis. Floral parts are morphologically well defined by two weeks preanthesis. In about 85 % of the flowers the basal, abaxial surface of two of the three bracts contains an outer involucral nectary; occasionally, none, one, or three nectaries are found. The maximum rate of increase in floral bud length occurs during the 24 hrs preceding anthesis. Flower opening occurs at about daylight, although light is not required. Multipored pollen grains germinate in about ½ hr after deposition on the stigmatic hairs. Fertilization is accomplished, for most ovules, by the end of the first day postanthesis. Stomata are abundant, particularly at the chalazal ends of ovules. Fiber initials (epidermal cells of the ovule) begin their elongation phase on the morning of anthesis and are bounded by a thin primary wall. Areas of contrast (spots) observed through the scanning electron microscope are speculated to be organelles “seen through” the relatively amorphous fiber wall, which lacks extensive fibrillar orientation of cellulose. Fiber elongation ceases by about 24–28 days postanthesis, and by 50–70 days postanthesis fibers are mature and exhibit a thickened secondary wall and spiral twisting. Concomitant with the time of fiber maturity, the ovary wall splits and opens along locular suture lines.     

THE WOOL-LIKE COVERING OF THE ROOTS OF LANNEA ALATA I. THE ORIGIN AND MORPHOLOGY OF THE WOOLY COAT

Lannea alata (Engl.) Engl., Anacardiaceae, a tree or shrub of East Africa, has roots covered with dense wool-like hair. Cork cambium of the root produces a closely appressed cork from which the hairs (modified cork cells) arise. Cork cells and wooly hair are rich in sterol and carotin-oid-like compounds and have thick walls. It is suggested that the root wool plays a role in the soil-air, soil-water relations of Lannea alata and other plants.     

MORPHOGENESIS OF THE STAMENLESS-2 MUTANT IN TOMATO. I. COMPARATIVE DESCRIPTION OF THE FLOWERS AND ONTOGENY OF STAMENS IN THE NORMAL AND MUTANT PLANTS

The single gene recessive mutant stamenless-2 (sl₂/sl₂) differs phenotypically from the normal (+/+) only in the stamen structure. Stamens of the mutant plants were laterally free, twisted, shorter, paler in color, possessed abnormal pollen, and bore naked external ovules (E.O.) on the adaxial surface near the junction of anther and filament. Mutant plants grown in the field during summer produced flowers in which a number of carpel-like organs (‘carpelloid stamens‘) with few or no E.O. replaced the stamens. On the other hand, plants grown in the greenhouse during winter possessed flowers with greater number of yellow and pubescent stamens and many E.O. Study of stamen ontogeny revealed that at initiation (up to 100 μ in length) stamen primordia of normal and mutant plants resembled each other. Thereafter the development of stamens in the two genotypes could be distinguished.     

THE DEVELOPMENTAL BASIS OF ANISOPHYLLY IN SELAGINELLA MARTENSII. I. INITIATION AND MORPHOLOGY OF GROWTH

The dorsiventral shoot system of Selaginella martensii is characterized by opposite pairs of ventral and dorsal leaves that are dimorphic in size and form. This study was undertaken to determine if the smaller dorsal leaf can be appropriately regarded as an arrested form of the larger leaf. Although the pattern of cell divisions and cell enlargement associated with leaf initiation is similar for both leaf types, the extent of localized growth results in distinctly larger primordia on the ventral side of the shoot. Ventral leaf primordia are also distinguished by the early formation of more extensive mesophyll tissue. Regression analysis of quantitative data on leaf length vs. position and leaf width vs. length indicates that the growth pattern of ventral and dorsal leaves is significantly different. These observations indicate that the developmental pathways of the dimorphic leaves of Selaginella martensii do not diverge at a relatively late developmental stage, but rather can be distinguished from inception.