Abstract
The effects of nitrogen, phosphorus and potassium on the so called "spike differentiation " and its development were investigated cyto-histologically, using " Satsukl " a variety of wheat. Sand culture was carried out with several kinds of nutrient solutions. Dr. ISHIZUKA'S culture solution which wvas used for physiological study of wheat plants was adopted as the standard and the following eight plots were provided, (1) PK, (2) 1/4NPK, (3) 3 NPK, (4) NK, (5) N3PK, (6) NP, (7) NP3K and (8) NPK, the control. The developmental process of wheat shoot apex can be devided into three main stages in terms of changes in form and structure. In the first stage the apex elongates gradually and its organization is not so evident. The inception of leaf primordia occurs slowly. In the second stage, the apex extends very rapidly and fundamental structure is established in it. This structure is characterized by the presence of three-layered tunica which mantles less-developed corpus or core. According to SHARMAN'S nomenclature these layers of tunica correspond to dermatogen, hypodermis and subhypodermis. The primordia of upper leaves and bracts initiate rapidly in this stage. In the third stage, the stratified layers of tunica receive some disturbances due to all directional division of cell, and results in the decreasc of the number of tunica layers. On the other hand, the number of cells in corpus becomes to increase becausc of the active all directional cell divisions in it. At this stage the form of apex changes shorter in length and broader in width. The differentiation of spikelct primordia begins in the middle of young spike at first and extends toward basipetal and acropetal directions successively and the apex itself turns to a terminal spikelct finally. Nitrogen, phosphorus and potassium are shown to have some specific effects on each developmental stage. Above all, nitrogen and phosphorus form a strong contrast in their effects. Nitrogen tends to accelerate the progress from the first stage to the second stage, but retards the transition to the third stage, delaying thc period of spikelet primordia differentiation. On the contrary, phosphorus tends to accelerate the transition from the second stage to the third stage and phosphorus deficiency delays the period of spikelet primordia differentiation remarkably. This relation suggests that phosphorus has an important physiological role in the transition from vegetative to reproductive stage in wheat plants. These results are basically the same as those obtained with rice plants.
