摘要:

SUMMARY1The flower is pentamerous. There is a five‐toothed calyculus and a perianth tube, which opens at the tip into five reflexed lobes and bears five epiphyllous stamens. The ovary is inferior.2The floral organs arise in acropetal succession.3The vascular anatomy of the flower is based on a pentamerous plan. The perianth tube receives five vascular traces each of which divides to form three to five bundles. The stamens receive one trace each, and five traces enter the style. In the stigmatic region they further subdivide into seven to ten bundles.4The anther wall is formed of four layers besides the epidermis. These are the endothecium, two middle layers, and the tapetum. The tapetum remains uninucleate.5The microspore mother cells divide simultaneously to form microspore tetrads of tetrahedral and decussate types.6The pollen grains are shed at the two‐celled stage. The division of the generative cell, which takes place in the pollen tube, shows clear spindle fibres accompanied by cell‐plate formation.7The archesporial tissue differentiates in the hypodermal layer at the bottom of the ovary cavity.8The megaspore mother cells give rise to linear tetrads of megaspores. All the megaspores except those lying towards the upper end are capable of further development. As a result of the enlargement and gliding growth of the megaspores the ovary cavity is soon obliterated.9The embryo sac is eight‐nucleate. The upper ends of the embryo sacs grow into the wall of the style, while the lower ends grow downwards so as to reach the pad of collenchymatous cells situated in the basal part of the ovary. A well‐developed embryo sac is approximately 22–28 mm. in length.10The first division of the egg is longitudinal. Owing to an extreme elongation of the suspensor the pro‐embryos are pushed down into the ovary. Only one embryo reaches maturity.11The endosperm is cellular and is initiated in the lower part of the embryo sac. Due to a dissolution of the separating walls of the embryo sacs all the endosperms fuse to form a composite mass.12There is no testa. The wall of the fruit comprises four layers of tissues. Of these the second (counting from outside), or the viscid layer, is very characteristic and is responsible for the ejection of the seed and

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1952.tb01557.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

SUMMARYThe flower comprises two trimerous whorls of perianth lobes, of which the labellum is supplied by four to six vascular strands and the rest by three bundles each. Some of the mesophyll cells become enlarged and contain raphides.The fertile stamen is quadrilocular. At the tetrad stage only the epidermis and the fibrous endothecium persist, while the two middle layers and tapetum disintegrate. The tapetal cells are uninucleate and the microspores remain together in tetrads. The pollen grains are bicelled at the time of shedding.The tricarpellary inferior ovary bears an indefinite number of bitegmic anatropus ovules arising from three parietal placentae. The hypodermal archesporial cell differentiates directly into the megaspore mother cell which gives rise to a linear tetrad of megaspores. The upper dyad cell rarely degenerates before the division is completed. In one instance a row of five cells was noticed. This might have arisen from two superposed megaspore mother cells or from an extra division of one of the megaspores.The chalazal megaspore functions. The mature embryo sac is usually six‐nucleate, probably due to a suppression of the last division of the two chalazal nuclei. The single antipodal cell degenerates early and may not be seen in mature embryo sacs. The two polar nuclei may fuse to form the secondary nucleus or degenerate without fusion.Syngamy occurs, but triple fusion is delayed or is omitted altogether so that there is no endosperm formation. The first division of the egg is transverse. The mature embryo is ovoid in shape and undifferentiated. It has no suspensor haustoria and is enclosed within the seed coat formed by the outer integument.Various abnormalities have been recorded. Evidence is presented to indicate that parthenogenetic development of the egg is possible and does occur in some ovules. In such embryo sacs the undischarged pollen tube is usually seen beside the egg, but parthenogenetic embryos have also been observed in embryo sacs that had apparently not received a pollen tube at all. These observations have been confirmed by chromosome counts during division stages of the egg as well as in cells of the pro‐embryo. Occasionally an embryo sac receives more than one pollen tube. Both the male nuclei of a pollen tube or the male nuclei of different pollen tubes may fertilize the egg, indicating the possibility of polyploid embr

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1952.tb01558.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1952.tb01559.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

SUMMARY1The stem apex of Syringa vulgaris L. has been examined.2The apex can be divided into a tunica and a corpus.3. Under another scheme of classification the apex can be divided into a central zone, a flank meristem and a file meristem.4. Leaves are initiated in the outer layers of the corpus.5. Procambium is produced by longitudinal divisions of cells in the inner layers of the corpus.6. The procambium supply of a leaf primordium is continuous at all times.7. Vacuolation of the leaf primordium tissues is first abaxial and then adaxial.8. The leaf primordium possesses an apical meristem.

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1952.tb01560.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY