LOCALIZED STAGES IN DEVELOPMENT. 121 



two-leaved is striking. On leading shoots of adult Arbor Vitae pointed leaves some- 

 times occur, often a quarter of an inch in length (Sargent, '91-97) , showing localized 

 reversions to the youthful and ancestral condition. These elongate leaves are not so 

 common or so marked in character as are the somewhat similar reversionary leaves of 

 the Red Cedar. 



Thuya gigantea. The seedling of the western species of Arbor Vitae {^Thuya 

 giyantea Nuttall) differs markedly from the seedling of T. occldentalis. In tliis species 

 (PI. 22, fig. 87), as shown by two specimens, there are two cotyledons 7 nnn. long, 

 2 mm. broad. The first nepionic leaves are a single pair, very short, 2 mm. long, 

 lying close above the cotyledons, and alternating with them in position. In the sec<md 

 whorl there are four leaves, considerably larger and alternating with the first pair and 

 cotyledons, as shown in the diagram (PI. 22, fig. 87a). Succeeding leaves on the main 

 stem are in four-leaved whorls until very near the top where they become somewhat 

 irregular. This is a marked difference from Tkuj/a occidentals (Figs. 84, 80) in which 

 no four-leaved whorls occur after the second nepionic whorl. Primary leaves are borne 

 on the main stem for a considerable period after "character" leaves have made their 

 appearance on tlie branches, as in Thuya occidentalis. The branches are more delicate 

 and more erect, forming a smaller angle with the main stem than in Tluiya occlden- 

 talis, where branches form almost a right angle with the main stem and are some- 

 what pendulous. On the brandies of Thuya gigantea there are two or three whorls 

 of primar}' leaves; but they are in twos instead of fours as on the main stem. The 

 character leaves are narrower and more pointed than those of T. occidentalis, but as 

 in that species they are comparable to the leaves of the Jurassic species of Thuyites. 

 In the adult the leaves have lost the acuminate tips seen in seedlings (Fig. 87) and 

 are ajipressed. The specimens described are seedlings from the Arnold arboretum 

 raised from seeds collected at Ashford, Washington. 



LiBOCEDRUS DECUEEENS. Seedlings of Libocednis decurrenx Torrey present inter- 

 esting features of development and variation. There were 25 seedlings in the lot 

 studied, raised at the Arnold arboretum from seed collected in Oregon; all were grown 

 under the same conditions. The seed were planted, Mar. 28, 1898, and seedlings were 

 studied, Sept. 17, 1898. The typical condition is represented in PI. 22. figs. 88, 89. There 

 are two long, strap-shaped cotyledons, 30 mm. long and 3 mm. broad. The first nepionic 

 leaves are a pair 12 mm. long and .75 nnn. broad, lying close to and alternating with 

 the cotyledons. Succeeding the two-leaved whorl after a considerable interspace there 

 is a four-leaved whorl which alternates witli tlie first whorl and cotyledons (Fig. 9). 

 Succeeding leaves are all in four-leaved whorls and are narrow, acicular, but large and 

 vigorous and of a bluish green color. Fig. 88 represents a i)lant in whicli all the leaves 



