NOTE ON THE OCCURRENCE OF ABNORMAL MEGAGAMETOPHYTES IN PINUS HALEPENSIS

Abstract

In June of 1959, one of us collected cones of Pinz~s halepensis from a tree growing on the campus of the University of California a t Davis. Ovules from the two cones of this collectioll were sectioned, and the resulting slides were added to the teaching collection of the Department of Botany a t Davis. Three of the first 14 ovules exanlined bore megagametophytes with archegonia in micropylar and chalazal positions (column 2, Table I), or in lnicropylar and lateral positioils (column 7, Table I). Additional gametophytes from ovules of the same collection were examined with a dissecting nlicroscope, and the positions of archegonia were recorded. Megagametophytes with archegonia a t the chalazal and micropylar ends were again detected. Three megagainetophytes with the cock's comb abnor~nality (Ferguson 1904) were also observed. The totals for all of the ovules examined from the first collection are entered on line a of Table I. In June and July of 1960, additional collections were made from the same tree (tree I) and from other trees on the campus (trees 11-VI). Megagametophytes from these collectiolls were examined with a dissecting nlicroscope. The results of these collections are recorded as lines b-k in Table I. The collections from tree I (lines a-c) represent ovules produced in two successive years. All five cones in these collections were taken fro111 the same portion of the tree. Only one of the five cones failed to yield abnormal megagametophytes. The observations made on ovules from tree I in 1960 increased the number of recorded variations in archegonial position (columns 3, 4, 8, 9, 11 of Table I) . Observatiolls made on megagametophytes of tree 11, which stands acljacent to tree I, further increased the number of variations observecl (columns 6, 10, 12 of Table I). The data for tree I1 are recorded on lines d-g. Tree I1 was sampled a t different levels and on opposite sides of the crown. A high percentage of abnormal megagametophytes was found a t only one location in tree 11. All three cones sampled a t this location contained abnormal gametophytes. Five of the nine cones sampled in tree I1 failed to yield any abnormal megagametophy tes. Trees I and I1 were both approximately 50 ft tall. Three other trees of this size (trees 111, IV, and VI) and one tree 15 ft tall (tree V) failed to yield cones containing abnormal megagametophytes. Trees 111-VI were widely separated from each other and fro111 trees I and 11. Samples from these trees were not taken in large numbers, because a refined estimate of the relationship of the percentage of abnormalities in trees I and I1 to tha t in all trees of P. halepensis on the campus was not intended. On an intuitive basis, i t appears