A number of cytological changes occur in rhizome transfer cells with age, the most striking being the appearance of microbodies each with a crystalline nucleoid and the presence of unusual plastids. Plastids in older transfer cells develop one or more electron-translucent regions and lack a defined thylakoid system. The number and size of vacuoles increases until ultimately one large vacuole is formed in old transfer cells. Accompanying these cytological changes in the cytoplasm the wall ingrowths change from being highly involuted and reaching a considerable distance into the cytoplasm of the cell to becoming thicker and less numerous, and finally form a rather uniformly thickened wall layer. The orientation of microfibrils in the thickened cell wall, resulting from the joining of the original wall projections adjacent to the tracheary elements, is random, while the wall thickenings away from the tracheary elements have more orderly arrangements of cellulose microfibrils.