Chloroplasts in situ are surrounded by jackets of a material which does not contain chlorophyll. The chlorophyll-bearing inner structure lacks motion while the jackets constantly change shape. Long protuberances may extend from the jackets into the cytoplasm and may segment into particles that cannot be distinguished from mitochondria. Segmentation and other dynamic characteristics of living plant cells have been recorded on cine film.

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Sunwiary. Bly uise of a micro technique for prodtucing extracts of spiInach mesophyll cells, chloroplasts were isolated in a state wherein they dlisplaye(l microscopically visible, reversible osmotic properties. Swollein spherical chloroplasts treatedl with hypertonic sucrose or mannitol media, bUt not NaCl, couild be shruinken to a state resembling their disk appearance in livinig cells. Reversible osmotic behavior was more easily demonstratedl when the chloroplasts were initially-isolated from cells in a relatively low osmolar concentration in contrast to uising 0.25 m1 suicrose or more concentrated media. Individual chloroplasts cotuld be swollen and contracted repeatedly throtugh as many as 4 cycles. The relationsh p between the capacity for osmotic behavior and chloroplast appearaince in cell extracts is dliscuissed.In the living higher plant cell, chloroplasts consist of a grantular, chlorophyllouis, stationary lamellar component suirrounded and, presumably, interpenetrated by a pleomorphic mobile phase containing stroma (4,6,21,22

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