1902 



VARIEGATION 



cbromatophores, and the various 

 -changes that these undergo, as the 

 leaf becomes oldei, produce the re- 

 markable and beautiful colorations 

 of this group of plants The col- 

 oration here, as in dracwnas and 

 caladiums, is Intensified by strong 

 light and nourishing food. The 

 more of the modified chlorophyll 

 there is produced and the more 

 rapid the changes in the modified 

 chlorophyll brought about through 

 the action of light and the acids 

 .and oxidizing ferments of the 

 leaves, the more highly developed 

 will be the colors, though here 

 .again high feeding is likely to cause 

 the plant to revert to its normal 

 condition. 



Variegated plants or parts of 

 plants are usually of slower growth 

 and smaller than green plants of 

 the same variety or the green parts 

 of the same plant. 



Causes of Variegation. Varie- 

 gation occurs either by bud -varia- 

 tion or by variations in seedlings. 

 In the former, a variegated branch 

 is likely to appear on an otherwise 

 perfectly normal plant. Such varie- 

 gations are easily reproduced by 

 budding, grafting or cuttings, but 

 generally do not develop again 

 from seeds produced on such 

 'branches. On the other hand, 

 when variegation develops in seed- 

 lings, the seeds of such plants usu- 

 ally give a number of variegated 

 individuals, even the cotyledons 

 being sometimes affected. In 

 some cases the proportion of varie- 

 gated plants from seeds is very 

 large and can be increased by selec- 

 tion. As a rule, the form of spot- 

 ting or marking n not constant in 

 seedlings, often being very differ- 

 ent from the parent. In certain 

 .groups of plants, which 

 have for many years been 

 selected on account of 

 the horticultural value of 

 these markings, the 

 variegated condition has 

 become almost a fixed 

 feature of the plant, as 

 in dracenas, caladiums, 

 codiseums, etc. While 

 the plants of these genera 

 re not usually propa- 

 gated from seeds, still 

 -when they are so propa- 

 .gated, a large number of 

 ^seedlings show more or less varie- 

 gation. 



Darwin and many of the earlier 

 investigators believed that these 

 variations were started in the 

 plant by unfavorable nutritive con- 

 ditions, and much has been written 

 on the subject as to whether or not 

 variegations should be considered 

 ;as diseased conditions. 



The question as to whether a 

 variegated condition could be 

 transmitted to normal plants by 

 budding and grafting has also 

 been much disputed, but the weight 

 of evidence indicates that in many 

 cases such transmission certainly 

 takes place. This has been thought 

 to indicate the presence of some 

 micro-organism, living either para- 

 :sitically or symbiotically in the 



2641. 



Kinds of variegation. Sansevieria 

 above and Caladium below. 



VARIEGATION 



plant, and causing the changes 

 known as variegation. 



Investigations conducted by the 

 writer on the so-called mosaic dis- 

 ease of tobacco, which is a form 

 of variegation, and also on many 

 other forms of ordinary variega- 

 tion, show quite conclusively that 

 the disease is not caused by micro- 

 organisms, but is due to a de- 

 ranged condition of the nutrition of 

 the cells. Without going into the 

 details of the matter, it may be 

 said that the condition is charac- 

 terized physiologically by a marked 

 increase in the oxidation processes 

 in the cells, caused by the presence 

 of an abnormal amount, er an ab- 

 normal activity, of oxidizing fer- 

 ment in the protoplasm. This fer- 

 ment prevents the movement of 

 food substances, especially starches 

 and nitrogenous materials. The 

 decrease of the latter is especially 

 marked, and it is probably on ac- 

 count of the lack of sufficient ni- 

 trogenous food that the cells do 

 not develop normally. The young 

 growing buds and dividing cells 

 require highly organized albumi- 

 noid foods. They do not make 

 use, to any extent, during the pro- 

 cess of growth and cell division, 

 of the ordinary nitrates which are 

 built up into nitrogenous foods by 

 the mature cells. The oxidizing 

 ferments, though normal constitu- 

 ents of all cells, prevent, when 

 they become excessively active, the 

 proper nutrition of the dividing 

 cells, and it is a curious fact that 

 when these ferments are extracted 

 from plant tissues and injected 

 into the young buds of healthy 

 tissues, they will, in the case of 

 tobacco at least, cause the buds so 

 treated to develop into variegated 

 shoots. The ferment in 

 question passes readily 

 through the cell-walls of 

 the plants and it thus be- 

 comes evident how such 

 changes could be trans- 

 mitted by grafting and 

 budJing, though no para- 

 sitic organisms of any kind 

 are connected with the 

 matter. 



Another method of producing 

 variegation of tobacco is by cutting 

 the plant back severely during 

 rapid growth. The new shoots 

 have to develop with a small sup- 

 ply of elaborated nitrogenous food, 

 the larger part being removed in 

 the severe cutting back. Shoots 

 thus developed nearly always show 

 variegation. The same thing is 

 true of many other plants, espe- 

 cially the potato, tomato, mulberry, 

 etc. In fact, it appears that a 

 plant is likely to show variegation 

 whenever it is so treated that the 

 growing buds or the forming buds, 

 or the seeds, have to develop un- 

 dersuch conditions that the ferment 

 content of the cells is increased 

 beyond the normal amount, and 

 the reserve foods stored are in 

 small amount. 



These changes must, therefore, 

 be considered as pathological in 

 their nature, as the vitality and 



