QUANTITATIVE INFLUENCE OF CORRELATION 207 



influences we term correlations. We can only speak with certainty of such 

 a condition when it can be proved experimentally, for in many cases the 

 construction of an organ stands in evident relation to that of another, but 

 we are unable to say whether this is direct or indirect. In the species of 

 Phyllanthus which bear leaf-like lateral branches the leaves on the chief 

 shoot are usually reduced to scales, but this result may be reached in 

 different ways : 



(a) The lateral shoot, which resembles a pinnate leaf, may directly 

 affect the primordium of the leaf arresting its growth, or 



(b] The foliage-leaves of the chief axis may become more or less 

 functionless because of the leaf-like construction of the lateral shoot and 

 therefore take on an arrested form. 



In the first case only is there a direct correlation. As it is of the 

 utmost importance for organography that such correlations should be 

 established. I shall in what follows cite some of the best-known examples. 



The influence which is exerted in correlation is either quantitative 

 or qualitative, but there is no sharp line between these. The quantitative 

 is the simplest and will be first illustrated. 



i. QUANTITATIVE INFLUENCE OF CORRELATION. 



Where quantitative correlation occurs either the development of the 

 primordium of an organ is entirely suppressed by another organ, or the 

 size to which it can attain is limited by the correlation. This quantitative 

 correlation has been also termed compensation of groivtli. 



Every plant-body forms more primordia of organs than it is able 

 to bring to maturity. Just as by far the greater number of seeds which 

 are annually formed are destroyed, sometimes because they do not find 

 favourable environment for their development, sometimes because they are 

 overcome by other organisms in the ' struggle for existence,' so also some 

 of the primordia of organs remain undeveloped because the plastic material 

 which they require for their unfolding is taken by others which exercise 

 a stronger attraction upon it. This rivalry appears as a ' struggle,' par- 

 ticularly in the formation of the propagative organs. The fruit in the case 

 of the oak, the beech, the lime, encloses a relatively very large seed ; in the 

 ovary a much larger number of ovules is found, as many as six in the oak, 

 and ten in the lime. The act of fertilization maybe effected within each of 

 these ovules and they are all capable of developing into seeds, and occasion- 

 ally more than one seed is formed ; but commonly at a very early period 

 one single ovule takes the lead and absorbs all the plastic material stream- 

 ing into the young fruit and the others are arrested in their development by 

 it and finally are suppressed. What causes determine which shall be the 

 favoured ovule are at present unknown, nor are we able to say whether that 



