Sjölund, R. D. “hanges in hloroplast tructure uring ifferentiation of hloem ieve lements and ylem essels from reen allus issue of treptanthus ortuosus”. cta icroscopica, ol. 1, no. 1, Mar. 1992, pp. 109-14, https://acta-microscopica.org/acta/article/view/16.