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(With Plates 1-4)The internal architecture of the grass shoot apex has been fairly thoroughly investigated * but although certain features of the external morphology have been described,! a broader study is needed, particularly from the point of view of what may be termed the biology of this region. In the present study, the morphological changes which the apex undergoes during its ontogeny are followed in dissected material of Agropyron repens (L.) Beauv. and the observations later used to elucidate some of the features commonly seen in various types of grass shoots. It is hoped that the investigation may also have a wider application in throwing light on, for example, problems such as those raised by the interest now being shown in grassland management and in programmes of cereal and herbage grass breeding based on the production of fertile amphiploids from sterile hybrids by the use of colchicine, etc.Agropyron repens was chosen because it provides an adequate range in apical morphology and also possesses a number of interesting features such as rhizomes, 'blind' shoots, etc. The choice was further influenced by an interest in Triticum-Agropyron hybrids, since it was felt that the present study has a bearing on the alternatives of annual, caespitose or rhizomatous habit which are bound to be considered if successful perennial wheats or superior wheat-couch grass forage types are to be obtained. MATERIALS AND METHODS {a) Dissection.Contrary to expectation, it was found that, with a little practice, it is not difficult to dissect out the shoot apex in the grasses. The fascination of actually seeing the living apex withthenewlyinitiatedprimordiain various stages of their early development amply repays any effort involved, and at the same time the method is ideal for building up a true mental picture of the three-dimensional shape of apices and primordia and the changes they undergo during growth. It is also a powerful corrective of impressions derived from the study of serial sections alone.Except for a microscope (preferably a stereobinocular) to be used during the last stages of dissection and the examination of the apex when it is uncovered, the only apparatus needed is an ordinary mounted needle and a hand-lens held in a rigid support. For the latter, a large reading glass in a clamp stand is excellent because it leaves the hands free and, if of about 7 cm. diameter or more, allows both eyes to view the material during dissection; a pair of short-focus spectacles might perhaps be substituted. With regard to

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