No abstract

Procecidochares utilis lays eggs on the stem apex of Eupatoriurn adenophorurn and on hatching the larvae tunnel into the stem. In response to the presence of the larvae a gall forms in the stem which may contain from 1 to 23 larvae. Callus tissue differentiates and divides to block the entry passages and seal the larvae in the stem. The normal development of the stem is halted and it swells as the pith cells continue to divide and become gall parenchyma. A layer of highly meristematic nutritive tissue develops around the larval cavity on which the growing larvae feed. New vascular tissue differentiates in the pith region of the gall around the larval cavity. Growth of the gall ceases when the larvae pupate, by which time most of the nutritive tissue has been consumed and the cells in the pith region have enlarged. Just prior to pupation the mature larva cuts a cylindrical tunnel to the edge of the gall, leaving only the epidermis intact; it then returns to the central cavity to pupate. The adult fly escapes by breaking through the epidermal 'window' at the end of the cylindrical tunnel.

No abstract

Summary Germination studies were made on Setaria chevalieri caryopses (seeds). The seeds imbibed readily upon moist incubation. An after‐ripening period which followed a cyclic patlern was necessary for maximum germination. Freshly harvested seed germinated in the presence of light, but only very sporadically in the dark. The germination of dark incubated seed was improved if the seeds were subsequently exposed to light. This photodormancy became less pronounced with dry storage. Treatment with red light increased germination. but was reversed by far‐red light suggesting that a phytochrome system operates in the seeds. Sodium azide treatments did not stimulate germination in the dark but were effective in the presence of light.

Whereas the gibberellin and inhibitor levels of potato (Solanum tuberosum L. cv. BP‐1) sprouts and stolons differ, their auxin and cytokinin levels apparently remain more or less unchanged. The levels of gibberellin in the sprouts is higher than that of the stolons; however, with regard to inhibitor levels the reverse is true. It would appear as if an internal balance of different hormones controls whether or not tuberization will occur. High gibberellin and low inhibitor levels (sprouts) may favour cell elongation and at the same time limit cell division. Decreased gibberellin and increased inhibitor levels (stolons) seems to favour cell division. As cell division is not retarded despite high inhibitor levels, it would appear as if the effect of the inhibitor is mainly directed at countering the gibberellins.