Ultrastructure of the Shoot Apex of Chenopodium Album and Certain Other Seed Plants

The ultrastructure of cells of the vegetative shoot apices is described for Chenopodium album, Kalanchoë blossfeldiana and K. laxiflora, Bryophyllum daigremontianum, Nicotiana rustica, and N. tabacum (Maryland Mammoth), and Ginkgo biloba. A less intensive study was made of the last three listed. The structures and organelles usually associated with meristematic cells were observed: dictyosomes, plastids (in various stages of development), mitochondria, endoplasmic reticulum (ER), vacuoles, lipid droplets, and plasmalemma. In addition, spherosome-like structures were observed in all zones of the shoot apices. Also, multivesicular bodies were observed in C. album and B. daigremontianum. Ribosome density is greater in cells of the flank meristem. Proplastids, plastids with prolamellar bodies, or grana have a differential distribution in the apex, characteristic for a particular species. Confirmation could not be given to the concept that vacuoles arise as a series of local dilations in long extensions of the so called "smooth ER." The tonoplast and ER are distinguishable at the time of inception of a vacuole, although the tonoplast may arise from the ER. Rapid growth of a vacuole and/or fusion with other vacuoles may result in irregularly shaped prevacuoles. No vacuoles were observed to originate from cisternae of dictyosomes in the species studied.