466 SCIENCE PROGRESS 



for the production of new buds, etc. Such a result is to be 

 expected if the phloem serve to distribute the assimilates to 

 places where they are required. 



The chief inferences to be drawn from the results of 

 experiments such as those described above are that the 

 parenchyma by itself is insufficient to conduct the organic 

 materials required for the growth of new tissues, that these 

 substances probably travel in the phloem and that the value 

 of laticiferous tubes either for conducting nutriment or for 

 providing a reserve supply is somewhat uncertain. The further 

 conclusion drawn by Czapek, that of the phloem elements the 

 sieve-tubes play the most important part in the conduction of 

 the assimilates as a whole, could hardly be regarded as beyond 

 question if it were based only on the experiments described 

 above. In none of these was it possible to study the conducting 

 properties of any one type of cell in anything like a satisfac- 

 tory manner, and therefore other methods of inquiry must be 

 considered. 



Chemical and Micro-Chemical Investigations 



In 1859 Sachs attacked the problem by means of micro- 

 chemical examinations of the amount and distribution of the 

 chief forms of plant food materials such as sugars, fat, starch 

 and proteids present at various periods during the germination 

 of seeds. The splendid work which he did in this manner 

 gave a new impetus to the study of plant nutrition and led 

 to a wide application of his methods to numerous other cases. 

 His conclusion that carbohydrates travel for the most part 

 through the innermost layer of the cortex has been mentioned 

 in the first part of this article together with Heine's criticisms. 



Later on, in his Text Book oj Botany (English translation, 

 1882, p. 91), Sachs appears to have been somewhat influenced 

 by the work of Briosi (1873) who, finding that starch grains 

 could be made to pass through sieve-plates by artificial pressure, 

 thought that this might also occur in the plant, and that in 

 this way the sieve-tubes served to conduct carbohydrates — an 

 opinion adversely criticised by Lecomte. In the passage referred 

 to Sachs attributes to the sieve-tubes the function of serving 

 secondarily for the transport of carbohydrates. Similarly in 

 his Lectures on Plant Physiology (English translation, 1887, 



