Specific Delimitation Research Articles

An Experimental Assessment of Some of the Characters Used for Specific Delimitation in the Genus Laminaria

The growth in culture of Laminaria saccharina (L.) Lamour. and a species from Nova Scotia, tentatively identified as L. agardhii Kjellm., has been compared. Several characters, normally used for specific distinction within the genus Laminaria, have been shown to be modified by environmental conditions. These all concern the lamina and include the following: general morphology and texture, the shape of the base, the anatomical construction and the presence or absence of mucilage canals.The question of the identity of L. agardhii from eastern and western Atlantic coasts is discussed.

Systematic studies of the anatomy of the genus Acrotriche R.BR. I. The leaf

The leaves of the 12 species of Acrotriche (Epacridaceae) have been examined anatomically from a systematic standpoint. It has been possible to distinguish between the species on the basis of leaf characteristics alone. These distinctions have been outlined in the form of a key to the species, and discussed fully in individual specific descriptions. The most valuable diagnostic characters are: presence or absence of papillose differentiation; shape of the leaf; shape of the sheath of fibres supporting the vascular bundle; presence or absence of a parenchymatous sheath around the bundles; and the presence or absence of calcium oxalate crystals and large fat globules. The specific delimitations based on the leaf anatomy agree with the morphological boundaries.

A Revision of the North American Species of the Genus Anisacanthus

Anisacanthus is a small genus of the Acanthaceae, which, because of the relatively few collections and the obscure specific characters, has been poorly understood. The present study was undertaken to correlate the morphological characters of the taxonomic entities of the genus as a whole, and to determine the relative value of the different characters in specific and varietal delimitation. Anisacanthus is one of several genera segregated from Justicia, having been described by Nees2 in the year 1842. He based it on Justicia qquadrifida Vahl,3 which in turn was founded on J. coccinea Cavanilles,4 a plant grown in the gardens of Madrid from stock brought from Mexico probably in the latter part of the eighteenth century. Vahl had changed the species name from coccinea to quadrifida because of the earlier J. coccinea Aublet. Under the name Justicia quadrifida Vahl, it was not infrequently cultivated in European gardens; and fortunately several authentic specimens from horticulture have been preserved in herbaria. Nees, however, soon changed the name of the type species to Anisacanthus virguclaris (Salisbury) Nees,5 and as such it was known until Standley revived the specific name quadrifidus.ff

A comparative study of species and strains of Helminthosporium on certain indian cultivated crops

Summary 1. Seven species or strains of Helminthosporium occurring on various cultivated grasses and one on ginger have been studied. 2. The symptoms of disease as seen in nature together with the morphology of the various forms under natural conditions have been described. 3. The eight fungi used were studied under different conditions of growth in artificial culture. The following were the main results : (a) Rate of growth depends on a number of factors, such as type of medium, amount of medium, presence or absence of light. There are certain strains, e.g. that from ginger, which show a slow growth-rate under all conditions tested. (b) The effect of temperature on growth also depends somewhat on the nature of the medium. The eight fungi show a certain amount of differentiation as regards the position of the optimal and maximal temperatures for growth and as regards sensitiveness to heating. (c) The macroscopic features of growth were found to vary very considerably. Details of the effect of cultural conditions on amount of aerial mycelium formation, colour formation, zonation, etc., are given in the text. (d) Certain microscopic growth features show a greater degree of constancy. Though amount of sporulation and spore measurements vary a good deal, spore shape and colour are markedly constant and therefore are of value for specific delimitation. 4. An extensive series of inoculation experiments was carried out with the following results: (a) Each fungus freely parasitises the host plant from which it was isolated. (b) Under artificial conditions at least, most of them are able to infect a number of hosts other than their own. (c) With the exception of two strains, all are able to produce the root-rot and foot-rot phases of disease in wheat and barley. (d) The intensity of the foot-rot and root-rot disease produced is markedly influenced by soil temperature, being greatest when the latter is in the neighbourhood of 30°C. 5. Of the eight forms studied, two have been assigned to new species. These are named Helminthosporium bicolor and Helminthosporium frumentacei . A strain from wheat is considered to be a variety of Helminthosporium halodes Drechs. and the strain from ginger to be Helminthosporium Maydis Nisikado and Miyake or a variety of the latter. The other forms are assigned to species already described. In the particular case of Helminthosporium Sacchari an amended diagnosis is given, with special reference to the size of the spores.