m ROBERT TRACY JACKSON ON 



Thaxter, Roland. 



'91. Tlie Coniiectieut species of Gymnosporangium (cedar apples). Bull. 1(17, Conn, agric. exper. .station, p. 1-6. 

 Wachsmuth, Charles, and Springer, Frank. 



'07. The North American Crinoidea Camerata. Mem. mus. comp. zool., vol. 20-21, 837 pp.. 83 pi. 

 Ward, Lester F. 



'87. Types of the Laramie flora. Bull. 37, U. S. geol. surv., 3o4~pp., 57 pi. 

 Ward, L. F. 



'88. The palaeontologic history of the genus I'latanus. I'roc. U. 8. nat. mus., vol. 11, p. .3!)-42, pi. 17-23. 

 Zittel, Karl A. 



'76-'90. Handbuch der palaeontologic. Jliinchen und Leipzig, 1870-00. (Invertebrates and plants, 3 vols., 261(i pp., 

 2100 figs. J. 



Explanation of Pi.ate.s. 



C = Cotyledons. 



Individual leaves or whorls of leaves are frequently numlicred a.s an aid to description. 



PLATE 16. 



LiRIODENDKON TULII'iriCU.V. 



Fig. 1. Typical four-lobed leaf of adult, xi. 1'. 04. 



Fig. 2. Typical six-lobed leaf of adult, representing liy dotted lines llie method of droiijiing ontof parts in the fonnatinn 

 of a reversionary leaf. A slightly regressive leaf omits two basal lobes a-b. a more regressive leaf omits four basal lobes 

 c-d, a highly regressive leaf is rounded distally e-f. Xi- P. 0.5. 



Fig. 3. Leaf with eight lobes, an extreme, progressive variation. X {. !'• 04. 



Fig. 4. Reversionary leaf of adult ; compare Fig. 2 c-d. X-i- P. 04. 



Fig. 5. Early uepionic leaf, with rounded angles and truncate end. X\- (lloliu, "Oo). P. 05. 



Fig. 6. Later nepionic leaf of a .seedling showing angles sharpened. X\. (Holm, '00). P. 95. 



Fig. 7. Reversionary leaves on mutilated branch of adult ; compare Fig. 2 a-b, and e-f. Xi. !'• 04. 



Fig. 8. Seedling .showing cotyledons and two nepionic leaves. X\- P. 03. 



Fi". 0. Branch showing progre.ssive variation of an abnormal tree in which P'ig 10 is the typical leaf. Leaf 1 has iwo 

 slight lateral lobes, leaf 2 has four slight lateral lobes, leaf 3 is regressive, comparable to Fig. 5. Xi. 1'. 05. 



Fif. 10. Typical leaf of a highly reversionary tree, comparable to nepionic leaf Fig. 6. Figs. 9-10 from tree in Arnold 

 arboretum. X i- I*. 95. 



Fi". 11. Seedling .showini; cotyledons and .succeejling nepionic leaves, leaf 3 has developed slight lateral lobes. Xi. 



P. 93. 



Fig. 12. Typical .six-lobed leaf of adult. Xi. P. 04. 



Fi". 13. Reversionary branch .showing leaves which in their simplicity ap])roach the condition eharacteri.stic of the 

 young ; compare with Fig. 11, also Fig. 2 a-b and e-f. X i. (Figs. 4, 7, 12, 13 are leaves from one tree. Cultivated, Dor- 

 chester, Mass. Figs. 8, 11, .seedlings, Milton, Mass.) P. 04. 



AlT.ANrilUS GI.A.NOri.OSA. 



Fii;. 14. Sucker from root of adult tree, all leaves alternate; 1-3 simple, 4. trifnliohite, 5-0 4uin.incfolinlatc. Culti- 

 vated. X i. P. 06. 



Fi". 15. Seedling showing romided cotyledons, the first nepionic leaves are opposite, later leaves alternate, all trifolio- 

 late. Leaflets of leaves 3-4 have marginal notches. Cultivated, x A. P. 'S>6. 



