The first part of the dissertation is dedicated to 

 plant development. In this part Wolff postulated in plants 

 the presence of "power, which is fluid collected from earth, 

 forced to act in the root, and distributed throughout the 

 plant, part of which is consumed in different places, and 

 part of which leaves the plant" ($ 1) . He called this power 

 "the essential power of the plant" ($ 4) . 



Before speaking about the effect of the essential power 

 on development, Wolff considered the structure of the young 

 rudiments of leaves, derived from buds. Using imperfect 

 optical means, he could nonetheless see distinctly that 

 this rudiment was derived from those structural formations 

 which exist in the formed leaf, namely the fibers and 

 vessels. The rudiment consists of transparent vesicles or, 

 as in the seed of a bean, of a light, homogenous substance. 

 At the beginning, vesicles are so few in number that they 

 can be easily counted, and Wolff found not more than twenty 

 in the young rudiments of the leaf. The number of vesicles 

 increases ("soon they become innumerable" $ 8) , while the 

 size of each vesicle remains as before, Very early, a few 

 vessels appear in the apex of the stem, the number later 

 increasing visibly. 



The formation of new vesicles and new vessels takes 

 place, according to Wolff, in the following way. The 

 delicate homogenous substance filling the spaces between 

 the vesicles is extended by the flowing nutritive juices. 

 As a result of this, rounded cavities are formed, producing 

 newly formed vesicles which are distributed between the 

 early vesicles. This same movement of the nutritive juices 

 builds canals in the homogenous mass which are transformed 

 subsequently into vessels ($ 21) . The formative ability of 

 the nutritive juice occurs during cessation of its movement, 

 when it is transformed by evaporation into a thick, then 

 viscous, and finally a solid substance. Wolff called this 

 character of the nutritive juice the solidification ability 

 ($ 27). 



Wolff pointed out that there is no preexisting structure 

 in the young rudiments of plant organs, because from the 

 beginning their formed substance, consists of a simple 

 mixture of substances and is deprived of any internal organiza- 

 tion. Only after this, the vesicles and vessels are formed in 



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