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This paper describes the changes undergone by the layer dividing the vegetative from the generative cell. The abundant contents of the space inside the membrane, consisting of opaque bodies, vary considerably as the pollen grain matures, and decrease in volumepari passu with the formation of the dense bodies in the plasm of the vegetative cells. The dense bodies constitute a layer of droplets surrounding the enveloping membrane of the generative cell within the cytoplasm of the vegetative cell. Connexions have been observed between the dense bodies and the partition layer which seem to indicate that the latter is apparently responsible for their organization, and is the area in which the synthesis of their contents takes place as well. The deposition of the dense bodies on the plasmalemma of the pollen grain points to their participation in the formation of one or other of the layers in which the grain is enveloped.

[EN]: A rib meristem is characterized by a complexus of longitudinal rows or ribs of cells which divide at right angles to the growth axis. This growth pattern is clearly represented in the cortex of the root. The longitudinal walls of the rib are primary longitudinal walls, the transverse walls being formed, basically, by middle lamella. At each division cycle, 2 daughter cells are formed, and the celt plate forms the new middle lamella between them. The fine structure of the cell plate formation has been studied by several authors TM. Moreover, FREY-WYSsLING et al. 2 showed that the middle Iamella formed by the coalescence of small Golgi vesicles, grew thicker through the supply of new Golgi vesicles. The aim of this paper is to study the development of the middle lamelta in relation to the cell division cycles., [ES]: La lámina media que separa transversalmente a las células del meristemo radical en columna se desarrolla, en virtud del aporte de pequeñas vesículas del aparato de Golgi, incrementando su espesor desde 0,1–0,2 hasta 0,4–0,5 µ. Las características morfológicas de estas paredes transversales permiten distinguir fácilmente las células hermanas y hasta las 4 células que se originan de 1 célula madre en 2 ciclos de división.

ARR et al. 1-3 were pioneers in the study which led to the discovery of a definite localization of the chromatin in relation to the nuclear membrane when they found that in the somatic cells of the cat the sex chromatiu is located at the nuclear membrane. BURGOS* demonstrated the accumulation of Feulgen reactive material on the inner aspect of the nuclear membrane in unfertilized eggs of Arbacia punetulata, and GA'x "5 studied the relations between chromatin and nuclear membrane outpocketings. However, the re]ation between chromatin network and the membrane in the interphase nucleus remains practically unexplored. In this paper we study a certain relation often observed between chromatin and nuclear membrane in the interphase nucleus of meristematic cells.

This paper reports the results of a study of the first beginnings of sporopollenin granules in the cells of the tapetum. The endoplasmic reticulum was observed to be the system responsible for their production, first by the formation of electron-dense bodies (pro-Ubisch bodies). These constitute the nuclei of the sporopollenin granules upon which laminae with the characteristics observed in the exine of pollen-grains are deposited in formation of the young Ubisch bodies. The latter ultimately assume a spherical shape (adult Ubisch bodies), whereupon they seem to be carried by channels across the cytoplasm of the tapetum into the locule of the pollen-sac. The origin, development and possible function of sporopollenin granules are discussed in the light of the theories and observations of other authors and of the writers themselves.