118 ROBERT TRACY JACKSON ON 



five or i*ix or more wliorls. The four-leaved whorls mark the second nepioiiic stage. While 

 this four-leaved whorl is chai'acteristic of the vertical axis, such whorls have not been seen 

 on any of tlie branches, even if given off very early. In Tliuya occidentalis, T. gigantea, 

 and Libocedrus decurrens (PI. 22, figs. 86, 87, 89) the two cotyledons are also succeeded by 

 one whorl of two leaves, then whorls of four leaves as described later. A third nepionic 

 stage in the Red Cedar is marked by another change. The four-leaved whorl is aban- 

 doned, and the leaves are arranged in whorls of threes (Fig. 5) . This occurs as early as 

 6 mm. above the two-leaved^ stage in some cases, or a little later in other cases. When 

 the three-leaved stage is introduced, no more four-leaved whorls are formed. Occasion- 

 ally branches on young plants have two-leaved whorls; these may be limited to two 

 or three whorls only, or may be of greater extent. While such occur, they are less 

 common, and three-leaved whorls are the characteristic feature of this period of develop- 

 ment. The leaves are flat, narrow, acuminate, distally ending in a sharp point, and they 

 are about 8-10 mm. long. This three-leaved acicidar character has been observed by 

 several naturalists; it is retained until the tree attains the height of a foot or more, 

 when adult characters appear, but the period of their introduction varies greatly in 

 individuals. In the adult the typical leaves are arranged in pairs, altei-nating in suc- 

 cessive whorls (Fig. 6). The leaves are blunt, scale-like, and closely imbricating. 



The above gives the features of leaves in the normal progressive development 

 of the Red Cedar. In the adult, variations are striking, as described by Emerson 

 ('46), Sargent ('91-'97), and others. In vigorous shoots (Fig. 7), given out mainly at 

 the ends of branches, the leaves are broad, elongate, distally acuminate, and arranged 

 in whorls of three or two leaves; but the former or ternate arrangement is perhaps 

 the more common. The dense tuft-like growths of adult Red Cedars, called " bird's- 

 nests," are still more obvious. They are caused by the growth of a fungus, Gymno. 

 sporangium nidus-avis Thaxter ('90), and are common at points where an injury has 

 taken place, as the cutting of a branch, on feeble or stunted trees, also on otherwise healthy 

 trees. It is distinctly a pathologic character. On these growths the leaves are long and 

 needle-shaped (Fig. 8) , and closely resemble the leaves of the young (Fig. 5) . The leaves 

 on these tuft-like growths ma}' be arranged in whorls of twos or threes ; but^three-leaved 

 whorls are present to a greater or less extent on all such growths and often predominate. 

 At West Chop, Martha's Vineyard, Mass., the soil is excessively barren and the situation 

 exposed. There the "bird's-nest" growths on the stunted cedars are very abundant. The 

 leaves on these, as in the vigorous terminal growths, are largely arranged in whorls of three 

 leaves. In Milton, Mass., where the soil is fertile, "bird's-nest" growths are less common, 

 and both in these and in vigorous growths two-leaved whorls predominate over three- 

 leaved whorls. At Cohasset, Mass., where the soil is good but the situation exposed, the 



