The role of environment on the dwarfing (short internode) phenomenon of apple (Malus domestisca Borkh.) was investi gated and defined in controlled environmental chambers. Orchard‐grown very dwarf, dwarf and semi‐dwarf trees obtained by natural sibcrossing of spur‐type cv. Golden Delicious and cv. Delicious, as well as standard cv. Golden Delicious, were propagated via in vitro techniques. Growth was rapid and none of the 4 types exhibited dwarf‐like characteristics when grown at constant 27°C with 12, 14 or 16 h daylengths. Standard and very dwarf plants grew at nearly the same rate at constant 30°C, whereas growth nearly ceased on both types at constant 35°C after 7 days. Dwarf and very dwarf plants responded differently from standard and semi‐dwarf plants when grown under alternating (ramped) night/day temperatures (15 or 20°C night ramped up to a daytime maximum over 8 h of 23, 28, 33 or 38°C, held for 2 h and then ramped down over 5 h to the night temperature). As the night/maximum day temperature differentia) increased from 0 to 23° under the ramping environments, growth of dwarf plants decreased markedly as compared to standard plants. When the same night/maximum day temperature differential occurred, the effect on decreasing shoot length was greater at the higher (20°C) night temperature. Increasing maximum day temperatures under the ramped environment also reduced leaf area plant−1 but did not markedly affect leaf number, resulting in short internodes. When a period of constant temperature was followed by ramped temperatures or vice versa, the sequence of constant vs ramped environments made little difference in the final growth of the 4 plant types. The data point to high temperature as the major factor for causing dwarfing of the sensitive plant types. Increasing the differential between night and maximum day temperature resulted in short internode. dwarf plants with small leaves similar to orchard‐grown dwarf trees.
The botanical and phytochemical aspects of P. aquilinum, as well as its toxicity to cattle in Bolivia were studied. Extensive colonization of the mountainous areas by the bracken fern viz. P. aquilinum var. aquilinum and P. aquilinum var. caudatum was recorded. Phytochemical analysis showed the presence of ptaquiloside in the bracken samples. The incidence of bovine enzootic haematuria (BEH) increased in the experimental area over the last 20 years. Cattle as young as 2 years old exhibited BEH. Dysphagia associated with alimentary tract tumours, as well as cachexia among the animals was observed. Pallid mucous membranes associated with urinary tract blood loss was also observed. Neoplasms were present in the bladders of all animals in the upper alimentary tract in 50% of the experimental animals. The bladder wall was thick and the mucosa was rough and hyperaemic, and contained angiomatous and solid tumour masses. Transitional cell carcinomas, angiosarcomas, fibrosarcomas ad squamous cell carcinomas characterized by epithelial plaques and profuse fibrous stroma infiltrated by inflammatory cells were observed.
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