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The Plant World. 



formation of chlorophyll. Occasionally shoots appear that are 

 immune to this virus and when grafted on chloiotic shoots re- 

 main green. If another shoot of a susceptible variety is grafted 

 on this one this second shoot will become chlorotic showing that 

 the virus passes unchanged through the immune form. 



That distinct morphological changes in the scion may occur 

 as a result of the specific influence of the stock is recognized by 

 almost everyone experienced in grafting, especially fruits, yet 

 conclusive results are not so easy to obtain. Records, however, 

 of observations and accurate measurements just published by 

 Waugh, give us some very definite information in this respect. 

 Waugh's observations were on various leaf and twig characters 

 and rate of growth, of scions of Milton plum grafted upon a num- 

 ber of other stocks. His careful measurements show a decided 

 difference in size and shape of leaves, and in the natuie of the 

 growth of the shoot of scions upon each of the different stocks. 

 These differences are constant for each variety used as a stock. 

 Of course in this and similar cases interpretation of the results 

 is always complicated by the difficulty of distinguishing between 

 variations due to some specific influence of the stock, or to mere 

 differences of nutrition supplied by the different stocks, for even 

 with a perfect graft union this latter could easily occur. How- 

 ever, were this the cause, similai modifications would occur on 

 anv stock if subject to the proper conditions of nutrition, and 

 this has not been found to happen. One of the most conspicuous 

 cases usually attributed to changed conditions of nutrition is 

 that of dwarfing, for example the dwarfing of pears when grafted 

 to the quince, or the apple when grafted on Paradise apple 

 stock. But even here we may entertain doubts as to whether 

 these results are not due to more fundamental causes than de- 

 creased nutrition. A fact often lost sight of is that by no varia- 

 tion of nutrition of a shoot on its own stock are we able to obtain 

 those modifications that often fallow when it is grafted to cer- 

 tain other stocks. While the maintenance of specific correlation 

 of the members of the plant body calls into activity various 

 nutritive processes, yet these can not be considered primary 

 causes, and in the unfolding and maintaining of specific form 

 and structure, and even function, specific influences more funda- 

 mental than and precedent to the nutritive processes are opera- 



