NATURAL INDIGO 65 



and lower respectively." " If the above explanation is correct 

 it is obvious that immense improvement in the plant can be 

 brought about by the selection and breeding of plants belonging 

 to the high content groups." 



It seems, however, from the recent work of Davis, that 

 Parnell's results may possibly be interpreted as indicating that 

 the soil on which his plants grew had various values for the 

 nitrogen content, so that his high- and low-value plants corre- 

 spond to low and high nitrogen contents. Nevertheless, it is 

 quite likely that certain varieties of each species of indigo 

 plant do give higher values for indican content than other 

 plants of the same species, just as the various species differ on 

 the average. To prove this, and to select high-yielding plants, 

 great care would have to be taken to secure absolute uniformity 

 in soil conditions, and, what is more difficult, in subsoil conditions 

 also, for the Java plant is deep-rooting. 



At present, therefore, the position appears to be that it 

 has been shown that indican content may be increased or 

 decreased by external conditions such as the poorness or 

 richness of the soil in nitrogenous compounds. Presumably 

 it varies also with inheritable qualities in the plant, which 

 quite possibly are connected with its relation to the root- 

 nodule bacteria, but no evidence free from uncertainty has as 

 yet been obtained on this point. 



The Feasibility of obtaining a Pure Strain of Indigo Plant 

 — As pointed out by Parnell and by Howard and Howard, the 

 floral mechanism of the indigo plant is such that cross-fertilisa- 

 tion is the rule. Examination of the stem colour of the 

 progeny of single plants showed how extensively cross-fertilisa- 

 tion took place. It was further found that plants protected 

 from insect visitors set but little seed. Hand-fertilisation 

 resulted in a larger yield. The above-mentioned workers have 

 also drawn attention to the possibility of sterility resulting 

 from continued self-fertilisation. Parnell concludes that the 

 failure of plants, raised by selfing for two generations, to set 

 seed at Sirsiah was quite possibly the result of this selfing. 

 Howard states that, so far as the evidence obtained at Pusa 

 goes, the indications are most definite that Java plants raised 

 from self-fertilised seed, even in a single generation, show a 

 marked falling off in size and general vigour. If an attempt 

 were made to purify Java hybrids and to obtain a plant breeding 

 true with high indican content, the experiment would, in all 

 probability, fail in a few years on account of self-sterility. 

 Thus, in order to try to produce a type of Java indigo specially 

 rich in indican — assuming that this quality is inheritable — it 

 would be necessary to obtain a number of plants of high 

 content and to carry on crossing inside this group, which of 



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