The Origin of Monocotyledons from Dicotyledons, 
through Self-adaptation to a Moist or Aquatic 
Habit. 1 
BY 
G. HENSLOW, M.A., F.L.S., F.G.S., F.R.H.S., V.M.H. 
Contents. 
SECTIONS. PAGE 
1. Introduction ..717 
2. Evidences from Geology ........... 718 
3. Distribution and Percentages of the Natural Orders of Monocotyledons as com¬ 
pared with those of Dicotyledons . . . 719 
4. Degeneracy of Monocotyledons .......... 720 
5. Possible Aquatic Origin of Palms.723 
6. Leaves of Large Size characteristic of many Aquatic Plants .... 724 
7. Water-storage Organs.724 
8. The Requirement of much Water by many Terrestrial Monocotyledons . . 724 
9. Cycads and Monocotyledons. 725 
10. Monocotyledonous Dicotyledons . . . . . . . . . 727 
11. The Effects of Water upon Roots ......... 731 
12. Origin of the formerly called ‘Endogenous’ Arrangement of the Cauline Bundles 
of Monocotyledons ........... 732 
13. The Forms and Structure of Aquatic Leaves are the Result of the Direct Action 
of Water. -735 
14. The Reticulated Venation of some Monocotyledons is only imitative of that 
of Dicotyledons.736 
15. Reproductive Organs.737 
16. Cytological and Embryological Investigations . . . . . . . 738 
17. Speculations on the Arrest of one Cotyledon ....... 74 ° 
18. Non-inheritance, Imperfect and Complete Inheritance, of Acquired Characters . 741 
19. Isolation and Natural Selection .......... 743 
20. Conclusion .. . 743 
1. Introduction. 
N EARLY twenty years ago (1892), I pointed out that there is a large 
number of coincidences between the morphological and anatomical 
characters of Monocotyledons and Aquatic Dicotyledons, sufficient, in fact, 
to justify the conception that the former class had been evolved from the 
latter. Beyond a limited extent in experiments upon adaptation, the 
1 Supplementary Observations and Experiments to ‘ A Theoretical Origin of Endogens from 
Exogens, through Self-adaptation to an Aquatic Habit’. Journ. Lin. Soc. Boh, xxix, 1892, 
P 4 8 5- 
[Annals of Botany, Vol. XXV. No. XCIX. July, 1911.] 
3 B 
