Morphologic Change as a Reflection of Adaptive Zone

The ratio of species per family in North American local mammalfaunas is lowest in Eocene time due to increased phyletic separationbetween surviving species. In respect to changes in adaptivezone, morphology may be relatively slow to change when an organismis using several different resources. If an organism's fitnessset is concave, morphology may not change to adapt to the newresource until it has become a significant proportion of itsresource set. Even when a resource has been important to theorganism for some time, there may be little morphologic adaptationto the resource.     

Oviposition behaviour and food plant discrimination in leafhoppers of the genus Oncopsis

Abstract. 1. Field host plants of the six British species of Oncopsis are described. O. avellanae is unusual in being associated with both Corylus and Alnus.
2. Laboratory experiments on nymphal feeding preferences, nymphal and adult survival, and adult oviposition preferences are described for all species, using Carpinus, Corylus, Alnus and Betula species as test plants.
3. All experiments demonstrated considerable specificity in feeding, and especially oviposition.
4. It is suggested that discriminative oviposition behaviour is the major determinant of observed field distribution patterns.     

Production and distribution of dry matter in maize following changes in plant population after flowering

Maize plants were grown singly in pots in a population of 3.7 plants m^-2, and 98 days after sowing (shortly after flowering) were arranged into three populations, 1.27 (W), 3.70 (M), and 6.15 (C) plants m^-2, respectively. The plants were harvested 131 days after sowing, about 4 wk before the normal time of maturity, because some plants at the closest spacing began dying. Increment of dry weight between days 98 and 131 was 373, 243, and 108 g/plant and grain dry weight at harvest was 218, 220 and 195 g/plant in populations W, M and C, respectively. Thus, dry weight of parts of the plant other than grain increased in population W, remained about the same in population M, and decreased in population C between days 98 and 131. Number of kernels per plant was c. 540 in all three populations. On day 98, immediately after rearrangement, leaf area index (L) was 2.0, 5.8 and 9.7 in populations W, M and C, respectively. By day 131 L had decreased to 6.7 in population C, but had hardly changed in the other two populations. Crop growth rate between days 98 and 131 was 101, 191 and 141 g m^-2 wk^-1, and grain dry wt per unit of land on day 131 was 277, 816 and 1196 g m^-2, in populations W, M and C, respectively.     

Nitrogen fixation and photoproduction of molecular hydrogen by Thiorhodaceae

Summary Nitrogen fixation has been shown to be a characteristic of two previously untested strains of the purple sulfur bacteriumChromatium sp.Chromatium strains have been shown to produce molecular hydrogen when suppliedD-L malate and bicarbonate in the presence of light and the absence of exogenous ammonia and molecular nitrogen. These results are discussed in relation to current findings on the nitrogen metabolism of the photosynthetic bacteria. Supported in part by grants from the Rockefeller Foundation, the Atomic Energy Commission, and the Research Committee of the Graduate School from funds provided by the Wisconsin Alumni Research Foundation.     

Root Contraction in Hyacinthus orientalis

Root contraction is effected in many species by redirected growthof parenchyma cells, supplemented in some cases by other processes.In Hyacinthus, root contraction is associated with the growthof inner cortical cells, which after becoming fully elongatedin the normal growth of the root, then expand radially and contractlongitudinally. The contraction is, however, a growth process,since it occurs in turgid tissue and is partly reversible byplasmolysis. Moreover, the radial walls of the cells concernedincrease in area and the cells increase in volume. The changes in cell shape associated with contraction involvechanges in cell-wall structure which, in so far as they aredetectable by polarization microscopy, are described and discussedin the light of current views on cell-wall growth.     

The role of the sheath tube in the development of expanding leaves in perennial ryegrass

A possible morphogenic effect of leaf sheaths on subsequent leaf development was investigated by varying sheath tube (pseudostem) length in plants of perennial ryegrass (Lolium perenne) cv. Talbot by either incising longitudinally or excising the distal portion of the sheath tube, while leaving the basal length of the tube intact. The tube was maintained at predetermined lengths by incising and excising new growth daily. The youngest rapidly expanding leaf was allowed to grow through the tube and was measured when fully expanded. Reducing tube length by excision or by incision from 60 mm to just above the cowl leaf on the apex reduced lamina length by 87% and 77% respectively. Over all tube lengths, laminae in incised treatments were almost twice as long as those in excised treatments. Sheath length followed a similar pattern. The effect on developing leaves of artificially extending sheath tubes (previously excised to 15 mm) to 30 or 45 mm with foil was similar to that of initially excising sheath tubes to 30 or 45 mm. The shorter the sheath tube (reduced by incision) through which the leaves had to grow, the shorter the cells, especially in the laminae. The estimated cell number per row along the length of the laminae ranged from 190 in tillers (shoots) with a very short tube (just above the cowl leaf) to 454 in intact control tillers. It is concluded that the sheath tube has a morphogenic influence on the development of subsequent leaves due to the change in environment of the leaf lamina on appearance, affecting both cell elongation and cell division.