THE AGRICULTURAL NEWS. 



January 



1911, 



FRUITS AND FRUIT TREES. 



BUD MUTATION AND THE DETERIORA- 

 TION OF CITRUS PLANTS. 



The Rural C'l/i/omian, ior October 1910, contains an 

 interesting article by Dr. .J. Elliot Coit, wliicli deals with the 

 relation that exists between ase.\ual or bud mutation and the 

 deterioration in characters that is found to take place in citrus 

 plants, particularly among the better kinds; that is those 

 which may almost be termed artificial varieties. 



The article, first of all, gives attention to the fact that 

 crossing is the most powerful cause of variation, particularly 

 when it takes place lietween male and female cells that are 

 very unlike in character, [t then goes on to mention the 

 variation which arises from changes in environment, giving 

 as an example the way in which the Washington Navel orange 

 from Florida becomes, in California, more acid, and acquires 

 better shipping qualities and a superior colour. 



In regard to the first cause of variation, it is pointed out 

 that this cannot possibly be effective in regard to most citrus 

 varieties of plants, as these are usually propagated by asexual 

 methods, particularly in the case of the better varieties; so 

 that some other e.\planation than this must be found, to 

 account for the ditt'erences that they are known to show from 

 time to time. 



In linding this explanation, attention is drawn to the 

 variation to which de Vries has given tiie name 'mutation'. 

 In explanation, it may be said that mutation difters from 

 variation in the following ways; (1) in being more pronounced 

 in character: (2) inappearing suddenly; and(:') inlicing capable 

 of forming immediately the oiigin of new varieties which may 

 have the power to transmit their characters to succeeding 

 generations. 



A full explanation of the phenomenon of mutation has 

 not been arrived at, so far. A mental picture which will 

 assist in obtaining some idea of its working may be obtained 

 by giving attention to the fact that all plants are composed 

 of cells; of these, only the vegetative cells need be considered 

 in the present connexion. The vegetative cells are ditt'erent 

 from the sexual cells in that they usually divide in a simple 

 way, giviiig rise to other cells which possess the characteris- 

 tics of the original ones. This is why plants propagated by 

 means of buds generally come true, as it is expressed. The 

 way in which mutation has its effect is as follows. It must 

 happen sometimes that, for some reason which is not)known, 



the dividing vegetative cells sulfer confusion as regards their 

 hereditary characters, so that the cells which they produce 

 are different from the original ones in possessing a new com- 

 bination of characteristics. Further, if this circumstance of 

 mutation takes place in the cells which make up the growing 

 point of a bud, it is ea.sy to see that the branch which is 

 formed by the growth of the laid will be wholly or partly 

 coni[)osed of cells possessing the characteristics of the muta- 

 tion, and in this way there is given rise to a bud mutation, 

 or sport, as it is often termed. The [>ractiral importance of 

 this is that if budwood is tidven from such a shoot, trees 

 will be obtained \\hich [jossess the new characteristics. 



As far as it has been possilile to make observations on 

 this matter, the conclusion is generally accepted that muta- 

 tions take place entirely by chance; there is no means of fore- 

 telling their existence, or of guiding them consciously in any 

 given direction. It will be interesting to consider, then, what 

 results may be expected from mutation. These are (1) sports 

 showing now characters which are neither objectionable nor 

 valuable: (2) sports having characters wdiich are unmistak- 

 alily objectionable; and (3) sports which have a nature and 

 properties superior to the variety of plant from which they 

 originated. 



As regards mutations which result in the production of 

 inferior varieties, the natural occurrence of these cannot 

 entirely account for the decadence that takes place in citrus 

 orchards, and the extent to which the inferior varieties attain 

 a distribution. It is in two ways that the practical work 

 conducted in orchards assists this distribution. Firstly, those 

 who are responsible for the cutting of budwood, to be 

 sent out where there is a demand for it, rarely take note 

 as to whether the material which they choose shows signs of 

 mutation, or not. Secondly, the pruning that is carried out 

 in the orchards seldom lias any regard to the special charac- 

 teristics of the branches that are being removed, or of tho.se 

 which are allowed to remain. If those who are responsible 

 for the pruning were to accustom themselves to seeing quickly 

 what branches are sporting toward inferior types, .so that they 

 may remove these wherever they were found, the deterioF- 

 ation consequent on mutation would be reduced, bj' this 

 means alone, to a very large extent. 



As will have been demonstrated by what has been said 

 already, the existence of mutations is not altogether 

 unfavourable to the agriculturist. There are those which 

 give rise to superior characteristics, so that an opportunity 

 is afforded of taking advantage of these, and obtaining 



