22 X^'BOPAGATIOW OF PLANTS. 



common in many of the forests of our Northern States. 

 The grain of these knots appears to be formed by cells 

 propelled by some cyclonic force that gave to them a 

 rotating motion, and yet there is a uniformity in this 

 distorted re-arrangement. Another peculiarity of these 

 knots is, that the bark coyering them always partakes of 

 the characteristics of the wood underneath and is fully as 

 variable in structure. 



But what may be termed the formative principle in 

 plants, is always a potent power, and while frequently ap- 

 pearing to promote abnormal growths, is equally power- 

 ful in assisting the re-arrangement of cell-matter for 

 continuing and perpetuating natural forms. The move- 

 ment and re-arrangement of cell-matter under artificial 

 conditions must have often been observed by all farmers 

 and gardeners, although probably few of those engaged- 

 in these pursuits ever think these phenomena worthy of 

 any special attention or study. An excellent illustration 

 of this movement or action of cells is often found among 

 the tubers of the common Potato, that have been stored 

 in cellars or pits where the temperature was a little too 

 high to insure perfect inactivity. An increase of tem- 

 perature a few degrees above the passive point tends to 

 incite action in the cells, and the most natural result 

 would be a growth from the eyes or buds, which very 

 frequently, if not generally, follows. But it is in the 

 abnormal growths that we obtain the best illustration of 

 the potency of the formative principle, as, for instance, in 

 the not unfamiliar production of new tubers on the out- 

 side or within large hollow Potatoes. No leaves, stems, 

 or roots are produced to assist the growth of these new 

 tubers, but the starchy cell- matter of the old Potato 

 moves inward or outward, as the case may be, and in re- 

 forming, builds up an entirely new structure out of the 

 materials obtained from the old. These new tubers, 

 nroduced in the absence of light, have well-formed buds 



