468 SCIENCE PROGRESS 



in substance under conditions which normally bring about a 

 consumption of reserves, and besides the latex practically no 

 other reserves exist in the seedlings. 



Similar experiments were made in 1887 by Leblois who 

 worked with the closely allied Scorzonera hispanica and was 

 led to express the opinion that under the conditions of his 

 experiments " the latex was a product of secretion and not a 

 reserve." 



Kniep also made a number of observations upon the latex 

 of Tragopogon floccosus^ Campanula media^ Vincetoxicum nigrum 

 and Chelidonium majits, seedlings of which he grew both in 

 darkness and in light. The results obtained seemed to him 

 to make the conclusiveness of Faivre's experiments still more 

 questionable. 



The changes in the constitution of the latex of Euphorbia 

 Lathyris between germination and production of seeds were 

 studied by SchuUerus in 1882. In addition he cultivated seed- 

 lings under various artificial conditions. From the results of 

 the whole of his work he drew the conclusion that latex is a 

 formative sap which is conducted in the laticiferous tubes. 



In the experiments hitherto described an apparent diminu- 

 tion in the materials contained in the latex was usually taken 

 to mean that some of these had been transferred to the sur- 

 rounding tissues to assist in their development. But as Kniep 

 points out, several other causes might bring about a consumption 

 of the constituents of the latex. For example the starch might 

 be employed in forming or regenerating the other organic 

 materials present, or in the construction of new protoplasm 

 and membranes for the tubes themselves during their own 

 growth, or finally it might be directly used up in respiration. 



In the light of these considerations the conclusions drawn 

 from experiments in which plants had been darkened for many 

 days appear rather unreliable. As a case in point, Treub's 

 experiments (1883) upon seedlings of Euphorbia trigona may 

 be given. Portions of the young stem and of the leaves were 

 darkened with tin-foil during periods varying from three to six 

 weeks. In very few cases did the starch completely disappear 

 from the laticiferous system, though the end branches of the 

 tubes became starch-free, as well as the other tissues of the 

 darkened stem. Apart from the pathological conditions which 

 must have prevailed, it is extremely difficult to tell from an 



