Pitting of Cells in the Carpocephalum Stalk of Conocephalum conicum (L.) Dum.

Abstract

In Conocephalum conicum (L.) Dum., primary pit-fields are preferentially located on the lateral walls of the cells comprising the proximal half of the stalk of the carpocephalum. In Conocephalum conicum (L.) Dum., sporangia are borne on a stalked receptacle, the whole mushroom-shaped structure being known as the carpocephalum. The initial growth of the incipient carpocephalum stalk occurs during the development of the archegonia on the carpocephalum receptacle. Following fertilization of the archegonia (in late spring) and during embryogenesis of the sporophytes, the stalk undergoes further growth by cell multiplication and cell elongation. We have designated this period of growth as the Phase One stage of stalk development. The resultant longitudinally aligned rows of parenchyma cells that are densely packed with starch grains become quiescent in the fall. In the following spring, the rapid cell-elongation growth activity of Phase Two is initiated and completed in a few days. The starch grains are digested and utilized presumably in the formation of new cell-wall carbohydrates. Functionally, the four to five centimeters of stalk elongation, due to the cell extension processes, elevate the sporangia on the receptacle-head of the carpocephalum. Once the spores are shed, the stalk (and the whole carpocephalum) becomes necrotic. Our investigation was restricted to the carpocephalum stalk in its Phase One stage of development. In this paper, we report the presence of primary pit-fields in the parenchyma cells constituting the tissue of the proximal half of the stalk. MATERIALS AND METHODS Specimens with carpocephala at the appropriate stage of development were collected from populations of Conocephalum conicum in the environs of The University of Michigan Biological Station. Immediately after a carpocephalum was dissected, its stalk was immersed in 10% Formalin buffered in 0.1 M potassium phosphate at pH 6.5 and fixed 24-48 hours. The fixed material was dehydrated in a tertiary butyl alcohol series, embedded in Bioloid paraffin (m.p. 60-62'C), and sectioned at 8 gm. Euparal provided a suitable mounting medium for phase-contrast photomicrography. OBSERVATIONS The carpocephalum stalk is composed of vertical files of parenchyma cells with a ring of small, cutinized cells at the periphery extending along the entire length of the stalk. For approximately half the length of the stalk (the proximal half), the cells possess primary pit-fields. In a longitudinal section viewed under phase-contrast optics, the pit-fields are clearly visible in surface view (Fig. I). They are preferentially located on the lateral walls. 007-2745/82/115-117$0.45/0 This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 06:12:36 UTC All use subject to http://about.jstor.org/terms 116 THE BRYOLOGIST [Volume 85