Expansion Of Cortex Research Articles

Evolution of the Felid Brain; pp. 243–254

Endocranial casts of 15 genera of fossil felids provide a record of felid brain evolution over the past 35 million years. Brains of the earliest felids, known as paleofelids, had coronolateral, suprasylvian and variably developed ectosylvian sulci as their only neocortical sulci. The last paleofelids, which became extinct around 8 million years ago, show little change in external brain morphology except for the addition of a presylvian sulcus. The other group of felids, the neofelids, appears about 25 million years ago, with coronolateral and suprasylvian sulci their main neocortical sulci, plus a discontinuous ectosylvian sulcus and small postlateral, sylvian and presylvian sulci. The posterior cerebellar vermis was straight and unexpanded. Beginnings of expansion of the sigmoid gyri and development of the cruciate sulcus are evident in neofelids 15–20 million years ago, and by 5–9 million years ago neofelids had brains that appear modern in external morphology. Endocasts of four genera of Pleistocene saber-toothed felids are similar in sulcal pattern to those of modern felids, except for Dinobastis, which had a unique expansion of visual cortex. Endocasts of 27 species of modern felids, representing the six commonly recognized genera, are strikingly similar in external morphology, although the brains of a few species, such as cheetahs, lynxes and jagouarundis, display distinguishing features. Modern felid brains average about the same size relative to body weight as do those of viverrids, but are about 25% smaller in relative size than those of canids. Olfactory bulbs are relatively smaller in felids than in canids or viverrids.

RADIATION DAMAGE IN APPLE SHOOT APICES

Pratt, Charlotte, John Einset, and Mohammad Zahur. (N. Y. S. Agric. Expt. Sta., Geneva.) Radiation damage in apple shoot apices. Amer. Jour. Bot. 46(7): 537–544. Illus. 1959.—Pattern of shoot growth and anatomy of the shoot apex of ‘Golden Delicious’ apple trees on ‘East Malling IX’ rootstock are compared in normal trees and those growing under chronic gamma irradiation (average doses of 17–48 r per 20‐hr. day) at Brookhaven National Laboratory. Bud damage in 6 varieties of apple trees is compared. Irradiated ‘Golden Delicious’ formed lateral buds on the current year's shoot, but the following year these buds grew into spurs which failed to form a terminal bud (“budless” spurs) and enlarged to form “club tips” and “swollen spurs” in this and subsequent years. Cells with thick walls and lightly stained cytoplasm occurred in shoot apices of irradiated lateral buds in mid‐June. The first tunica layer was more resistant to radiation than the inner tunica layers and the corpus; pith rib meristem was still more resistant. Inflorescence and floral meristems were rarely found, but once formed, continued development. One‐year‐old budless spurs had a few leaves but neither an organized apical meristem nor leaf primordia. Surface of the apex was often folded. Periderm and, later, deep‐lying wound cambium developed. Expansion of pith, vascular tissue, cortex, wound cambium and periderm caused enlargement of club tips and swollen spurs. Many lateral buds from the gamma field which were propagated without irradiation in early August grew into long shoots with terminal buds. Scions removed from irradiation in November and inserted into normal trees showed lower survival and many of their shoots were budless. This suggests that the capacity for normal growth of a bud damaged by chronic irradiation is greater in mid‐summer than later in the year. With reference to percentage of budless shoots, ‘Delicious,’ ‘Golden Delicious’ and ‘McIntosh’ were more sensitive to an average dose of 24 r per day and lower doses than were ‘Cox,’ ‘Macoun’ and ‘Spy.’ Symptoms of radiation damage in apple buds during the first year were similar following acute or chronic irradiation. Degree of radiation damage, as expressed by death of apical meristems, was concluded to vary with stage of development of the bud, structure of the apical meristem, and genetic constitution.