| Abstract: | Abstract Histological and anatomical modifications in the root apex of PINUS PINEA L. seedlings grown in vitro from immature seeds, in the dark. — The seeds of Pinus pinea L. take three years to develop reaching maturity during the spring of the forth year. Immature seeds were collected at successive stages and cultivated in vitro in Heller's medium. The seedlings showed atrophy of the root togheter with histological and anatomical modifications of the root apex and formation of a small tuber. The extent of these modifications depends on the age of the seed and on how long the seedling is cultivated in vitro. Seedlings derived from seeds planted on August 31st and kept in vitro for about a month had an atrophic root through lack of meristematic capacity; in it the secretory and conducting apparatuses had developed but with mixed radical and hypocotilar characters. Seedlings from unripe seeds planted on September 30th and kept in culture for about one month showed an atrophic root owing to a rapid process of differentiation accompanied by the formation of isolated tracheid-like elements and of discontinuos vascular strands very near to the apex. Lateral proliferations gave rise to masses of various size of unorganised parenchyma which could separate the cortical and cap parenchyma from the central cylinder. In some cases the root cortex, clearly recognisable owing to an advanced process of differentiation, cut off from the central cylinder the root cap cells which degenerated. Seedlings obtained from seeds planted on October 11th and kept in culture for about one month showed a radical tubercle deriving from fasciation of the main axis which had ceased growing and had formed various abnormal lateral root primordia. |
