INVESTIGATIONS ON RESISTANCE OF OATS TO STEM EELWORM, DITYLENCHUS DIPSACI KÜHN

A procedure adopted for testing many varieties of oats and segregating progenies for reaction to attack by stem eelworm ( Ditylenchus dipsaci Kühn) is described, and its merits and limitations discussed in relation to the breeding of resistant varieties.
A study of some 250 forms of oats revealed new sources of resistance in cultivated and wild species. New sources of resistance in the cultivated species Avena sativa were found only in winter types, and in the other hexaploid species in forms belonging to A. byzantina (C) Koch, and the winter wild oat A. ludoviciana Dur.
Segregate progenies in advanced generations could be selected in the field by their reaction in a single drill in the first year followed by a head-row progeny test in the next season. Reaction was sufficiently well defined to identify the truebreeding resistant and susceptible lines.
The inheritance of reaction to stem eelworm in crosses involving Grey Winter and susceptible types depended on a single factor pair with resistance dominant.     

ELECTRON MICROSCOPIC STUDIES ON THE OOGENESIS OF DRAGONFLY AND CRICKET WITH SPECIAL REFERENCE TO THE PANOISTIC OVARIES

The successive ultrastructural changes during oogenesis in Sympetrum frequens (Odonata, Libellulidae) and Gryllus yemma (Orthoptera, Gryllidae) were studied.
The structures of the terminal filament and boundary between the terminal filament and the germarium differed from each other in these 2 species; in Sympetrum the boundary between the terminal filament and the germarium was a special acellular transverse septum, whereas that in Gryllus was composed of several flattened cells which seemed to be similar to the prefollicular cells in the germarium.
During the previtellogenesis, the nucleolar extrusions and emissions of the outer nuclear envelope were observed frequently in young oocytes. In Sympetrum , electron dense masses were observed in the oocyte cytoplasm, which seemed to be yolk nuclei or Balbiani bodies and were composed of aggregated small particles (about 200 A in diameter). They were gradually dispersed in the cytoplasm until the onset of vitellogenesis.
In both Sympetrum and Gryllus , yolk precursors seemed to be incorporated into oocytes by micropinocytosis as observed in various animals.
The egg membranes, viz. , the vitelline membrane and the chorion, seemed to be formed by products from follicle cells which developed rough-surfaced endoplasmic reticulum and Golgi bodies. Thus, both of these egg membranes were assumed to be the secondary egg membranes.     

ULTRASTRUCTURE OF THE GREEN ALGA DICHOTOMOSIPHON TUBEROSUS WITH SPECIAL REFERENCE TO THE OCCURRENCE OF STRIATED TUBULES IN THE CHLOROPLAST1

The ultrastructure of the siphonous green alga Dichotomosiphon tuberosus (A. Br.) Ernst is compared with that of other siphonous plants. There is a characteristic association between the Golgi bodies and endoplasmic reticulum, but. the mitochondria are not involved in the association as they are in Vaucheria and the phycomycete Saprolegnia. An unusual structure and arrangement of the chloroplasts is described as well as a previously unreported type of “striated tubule” which occurs in most if not all chloroplasts, and amyloplasts. The structure of these tubules is compared with that of other tubules recently found in green algae and higher plants. In addition, cytoplasmic microtubules arranged in the longitudinal direction of the siphon suggest a function in cytoplasmic streaming.