LEADING PRINCIPLES OF SCIENCE. 11 



and from the regular-flowered crowfoot to the distorted monks-hood by a series 

 graduated in like manner. 



16. NATURA NON SALTUS FACIT, said Linnaeus, in evident allusion to this bean- 

 tiful principle, which will constitute one of the most interesting themes of botanical 

 studv. 



17. ACCOMODATED FORMS or organs is a phrase applied to another principle 

 in the Divine plan, the reverse of the first. This principle appears in the adaptation 

 of different organs hi different species to one common use ; of which there are many 

 familiar 



18. ExAifPLES. Thus, the slender vine requires support. Now it throws out a 

 tendril for this very purpose, grasping whatever object it may reach, as in the grape. 

 Again, the prolonged leaf-stalk answers the same end, as in Clematis. Again, tho 

 supple stem itself, by its own coils supports itself, as in the hop ; and, lastly, ad- 

 ventitious rootlets in the ivy. 



19. ANOTHER ILLUSTRATION. Reproduction is the general office of the seed ; 

 but this end is also accomplished, in different species, by nearly every other organ, 

 by buds, bulblets, bjulbs, tubers, cuttings, scions, and even leaves. 



20. ANOTHER. This principle is also traced hi the nutritious deposits of plants, 

 which are generally made in the fruit ; but often tho root serves as the reservoir in- 

 Ht ;>a 1. or even the stem. And in caso of the fruit, the rich deposit is now found in 

 the pericarp of the peach, tho calyx of the apple, tho receptacle of the strawberry, 

 the cotyledons of the almond, tho bracts, flower-stalks, &c., of tho pine-apple. Thus 

 God's boundless resources of skill can accomplish either one purpose in a thousand 

 different ways, or a thousand different purposes by a single organ. 



21. ARRESTED FORMS. This principle, demanding a wider range of generaliza- 

 tion than either of the foregoing, we state rather as a hypothesis, that the student 

 may hereafter test its probability by his own observations. The flowering plants 

 which clothe the earth hi such numbers, constituting the apparent vegetable world, 

 are hi truth but a minor part of it in respect to numbers. Numerous tribes, of lower 

 rank, embracing thousands of species, ro^cli far down the scale, beyond the utmost 

 limits of the microscope. Now a principle of analogy seems to pervade these ranks, 

 called the principle of arrested forma, binding all together in one consistent whole, 

 proving that for the vast realm of vegetation there was but one plan and one origin. 



22. THE HYPOTHESIS STATED. The successive tribes of vegetation, beginning 

 with the lowest, have each their type or analogue hi the successive stages of em- 

 bryonic growth in the highest tribe. 



23. MORE EXPLICITLY : tho, flowering plant, hi the course of its growth from 

 the pollen grain to the completed embryo, passes necessarily through a series of 

 transient forms. Now, suppose the development of the plant arrested at each of 

 these stages, so that these transient forms become permanent, we should have a 

 series of organisms analogous to the various tribes of Flowerless Plants ; the Pro- 

 tococcus, e. g., an arrested pollen grain ; the Oscillaria, an arrested pollen tube ; and 

 so on up to the Marsillea, whose organization answers to that of the full-formed 

 embryo of the flowering plant. Thus we might truly say of the lower plants that 

 they are the arrested forms of the higher. 



24. INDIVIDUALITY OF THE PLANT. The plant is both material and immaterial. 

 Its form and substance is the material, its life the immaterial The material com- 

 mences existence as a single cell, and is ever changing. The immaterial gives to 

 that cell its individuality, and fixes inevitably its law of development, so that it 

 must grow up to become such a plant as it is, and by no possibility any other. 



25. ILLUSTRATION. The embryonic cell of a rose may not differ materially, in tho 



