MOVEMENT AKD EEOEG iNIZATIOlir OF CELLS. 23 



ance. It may be that only one or two degrees above the 

 freezing point is all that is necessary to promote action 

 in the vegetable cells of cei*tain plants indigenous to 

 cold latitudes, stUl, this is just as indispensable as sixty 

 or seventy degrees higher temperature is for producing a 

 similar movement in the cells of those inhabiting tropical 

 climates. 



It is to this movement of cell-matter, in response to a 

 stimulant, that we are indebted for all the benefits and 

 advantages derived from the artificial methods of propa- 

 gating plants. The gardener's art consists principally 

 in taking advantage of what he has here learned in regard 

 to the natural functions and properties of plants. 



The uniformity of the movement of ceU-matter has 

 enabled the propagator to formulate certain operations 

 in order that they may be conducted under uniform 

 conditions, and for the express purpose of producing 

 uniform results. Under certain conditions, he is enabled 

 to make the cells of one plant throw out new cells which 

 unite firmly with those of another, thereby admitting of 

 the passage of fluids, as in the operations known as bud- 

 ding and grafting. But under other and different con- 

 ditions, this exuded cell-matter may become roots, cap- 

 able of absorbing nutriment directly from surrounding 

 elements in the soil, or, as in the case of the true epi- 

 phytes, from the atmosphere. 



In the formation of knots on ligneous plants there is 

 certainly a deviation from natural channels in the de- 

 positing of ceU-matter. A few cells at first, through 

 some obstruction or disturbing cause, are forced out of a 

 direct course, and the next layer of woody tissues de- 

 posited must pass over or around the obstruction, this 

 being repeated year after year, until the entire abnormal 

 structure is complete and built up, in many instances, to 

 an enormous size ; for Ash-knots two to three feet in 

 diameter, and weighing a hundred pounds, are not un- 



