Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The effect of forest density on minimum temperature was measured in several Abies religiosa forest quadrants located in and near colonies of the monarch butterfly (Danaus pexippus), in the Neovolcanic Belt of Mexico. Regression analysis with forest density, altitude and date of the studies show that the minimum temperature is an inverse function of forest density. The date of the studies and the altitude were also important components of the model. The lower temperatures in harvested (thinned) forests are explained by the absence of tree structures that prevent the escape of heat due to radiation during the night. Using the regression equation, we can predict that temperatures in forests that have been radically thinned will be more than one degree Celsius lower than in areas where butterflies have established their colonies. A subsequent drop in temperature of this magnitude, which is already at the death limit for butterflies during some winter storms, would surely increase colony mortality considerably.

A hierarchy of phenological features defines the opportunities for breeding in a population of Cnidoscolus spinosus in a tropical deciduous forest in western Mexico. On any one tree, inflorescences develop in rough synchrony and all present flowers of both sexes. Only female flowers develop at the lowest ranks of ramification but only males develop later. Overlap of the mature period of flowers of both sexes is uncommon on one inflorescence of between inflorescences : individual trees are functionally female or male at any moment. lnter-tree synchrony may thus reduce successful breeding. Asynchrony is achieved in part by differences in the onset of flowering, but also by variance in the lenght of individual flowering cycles. The occurrence of two or three cycles per tree during one season for the population increases its breeding opportunities.

An anatomical study of the resin canals of the bark of the main stem, branches, young stems and shoot tips was carried out in two species of Bursera: B. copallifera (Sessé & Moc.) Bullock and B. grandifolia (Schl.) Engl. Through hand dissections, the types of channels and their distribution in the main stem and branches were studied, finding that both species have axial, radial and tangential channels. The latter are connections between axial channels or between axial and radial channels; thus the three types of channels form a single network in the functional and non-functional phloem. Subsequently, the samples were embedded in paraffin and stained with safranin and fixed green, observing that in both species the axial canals in the primary body originate from schizogenic spaces. In B. copallifera the radial channels of the xylem pass into the phloem through the cambium, keeping the number of epithelial cells constant in them. Tangential channels are abundant in the secondary cortex of both species.

The altitudinal distributions of members of the genus Pinus were studied on mountain ranges in the western United States and Mexico. The community of pines on each mountainside consists of members of three major groupings - long-needled Diploxylon species, short-needled Diploxylon species and Haploxylon species. Long-needled Diploxylon species form a core sequence of altitudinally replacing species over whose distribution are superimposed sequences of members of one of the other two groups. In the northern mountains ranges Haploxylon species formed this second sequence while in the southern ranges short-neddled Diploxylon species assumed this role. Some morphological characteristics of these species were examined and random associations of species pairs generated using these characteristics. The results suggest that resource partitioning between altitudinally associated species does not occur but rather that a successional situatton exists with long-needled Diploxylon species being replaced by either Haploxylon in the norrhern ranges or short-needled Diploxylon species in the southern ranges.

The photosynrhetic characteristics of planes native to a Californian hot desert habitar, Death Valley, and a cool coastal locality, Bodega Head, were compared. The desert planes showed a variety of responses including species with C3 and C4 photosymhetic pathways, drought tolerance and inrolerance, a wide range of thermal optima, and biochemical and morphological thermal acclimation. Most of the desert species have high photosynrhetic light requirements for saruration and high photosynrheticcapacicies.

A new species of Euphorbiaceae, Jatropha chamelensis, from Jalisco, Mexico is described and illustrated. lt belongs to Section Mozinna (Ort.) Pax, Subsection for its large, broad, non peltate leaves, glaucous underneath. An anatomical description of the wood is included.

Three name combinations far North American Lycium: L. macrodon var. dispermum, L. nodosum var. isthmense, L. parishii var. modestum, L. fluberulum var. berberidoides, and a new variety: L. californicum var. interior, are proposed.

A new species of Decazyx (D. esparzae, Rutaceae) from Tabasco and Veracruz is described. The new taxon is a small tree of the rain forests of southeastern Mexico. The only other known species in this genus is D. macrophyllus from Honduras.

In the course of a taxonomical revision of the genus Phaseolus and considering the recently important research realized in the Phaseolus-Vigna complex, where the palynological attributes for the genus were precised, the present paper describes the pollen of Phaseolus chiapasanus Piper. The large-size class pollen grains of Ph. chiapasanus are tricolporate, brevicolpate, pseudo-operculate; semitectate, and widely reticulate. The structure of the infratectum could be considered of the granular-collumelar type. Some of the attributes found in the polen of Ph. Chiapasanus were not known for the genus, though such attributes are commonly found in the subgenus Sigmoidotropis of the genus Vigna. Ph. chiapasanus shows a series of morphological and palynological differences that open the possibility for the creation of a new section within the genus. More detailed studies will definitely by needed to better document relationships to other species of the genus.

The results of chromosomal studies reported for species of Lycium of the world are presented. Meiotic chromosome numbers were determined from pollen mother-cell squashes of North American taxa of Lycium. In a single case, a mitotic chromosome number was determined from the radicle of a germinating seed. The taxa studied were: L. andersonii Gray var. andersonii, L. andersonii var. deserticola (C. L. Hitchc.) Jepson, L. andersonii var. pubescens S. Wats., L. andersonii var. wrightii A. Gray, L. berlandieri Dun. var. berlandieri, L. berlandieri var. parviflorum (Gray) Terrac., L. berlandieri var. peninsulare ( Brandeg.) C. L. Hitchc., L. brevipes Benth. var. brevipes, L. californicum Nutt. ex Gray var. californicum, L. californicum var. Arizonicum A. Gray, L. californicum var. interior Chiang, L. carolinianum var. Quadrifidum ( Moc. & Sessé ex Dun. ) C. L. Hitchc., L. cooperi A. Gray, L. macrodon A. Gray var. macrodon, L. nodosum var. isthmense ( Chiang) Chiang, L. pallidum Miers var. pallidum, L. parishii A. Gray var. parishii, L. parishii var. modest1tm ( I. M. Johnst.) Chiang, L. puberulum var. berberidoides ( Correll) Chiang, and L. torreyi A. Gray. Chromosome numbers of n = 12, 24, 48, 60, and 2n = 24 were found. It is concluded rhat x = 12 is the base chromosome number for Lycium. The origin of n = 18, previously reported, is discussed.