Cellular development in the leaf
Collier, J. A.
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The subject of this investigation is the development of cells in relation to the general development of the leaf in wheat. At a certain stage in the development of the leaf cells are being generated from an intercalary meristem; this situation was first accurately described by Lehman (1906). Such a development is essentially different from that of the dicotyledonous leaf in which divisions may be randomly distributed over the leaf or may be restricted to groups of marginal initials. In the Gramineae where the leaf is generally lanceolate or filiform there tends to be a localised meristematic zone at the point of insertion of the leaf on the stem or at the point where the lamina is attached to the leaf sheath. This intercalary meristem produces cells which become incorporated into the body of the leaf and which themselves extend the length and area of the leaf. The time over which the meristem is active is restricted and tends to be confined to the phase of early development. At a certain point, activity in the meristem ceases and thereafter continued growth of the leaf is due to the expansion of the cells which have already been formed. When the meristem is active, cells at different parts of the leaf are at different stages of development. In general, cells are at progressively advanced stages of development as distance from the base of the leaf increases. Clearly this situation resembles, in certain respects, the situation in the apical zones of the root and shoot, and it may be possible to study cellular development in the leaf with the techniques that have already been applied to the root and shoot. On the other hand, since the intercalary meristem is only active over a limited period the study requires an analysis of the growth of the leaf as a whole.