154 TRANSLOCATION IN PLANTS 



lyzing agent. Various types of storage and receiving 

 tissues were tested, including cotyledons and the developing 

 seedlings, tubers and their sprouts, bulbs and their develop- 

 ing leaves and roots, and old leaves of Bryophyllum and 

 Byrnesia and the plantlets developing from them. 



As shown in Table 19, the receiving tissues in all instances, 

 and by three methods of testing, had higher osmotic con- 

 centrations than the supplying storage tissues. Not only 

 have the receiving tissues the higher osmotic concentra- 

 tions, but the data from the onion (given in the original 

 paper but not here) show a progressive change in concen- 

 tration increasing from the older outer scales toward the 

 younger scales, with the highest concentrations in the grow- 

 ing tissues which are receiving solutes from the storage 

 scales. The outer scales with lowest concentration empty 

 first and lose their contents to tissues with higher con- 

 centrations. That the osmotic concentration gradient is 

 always in a direction the reverse of that demanded by the 

 Miinch hypothesis has not been demonstrated. But in all 

 of these determinations where the supplying tissue was a 

 storage tissue and the receiving tissue a growing organ, 

 the concentration gradients have been in the wrong 

 direction to satisfy the Miinch hypothesis. 



Only under special conditions, where the receiving cells 

 may have highly extensible walls and are therefore inca- 

 pable of developing much turgor, or where the receiving 

 cells are exposed to a desiccating environment reducing 

 their turgor, would it be possible for them to maintain a 

 higher osmotic concentration than the supplying cells and 

 still receive solutes by the proposed mechanism. Ursprung 

 and Blum (1924) have given evidence that growing cells 

 are likely to have low turgor pressures, although the low 

 turgor pressure actually calculated may have been excessive 

 and may have resulted from release of pressures incident 

 to cutting the tissues for observation (Curtis and Scofield, 

 1933). The second alternative, that is a desiccating 

 environment, seems highly improbable. Even an assump- 

 tion that the receiving cells have highly extensible walls 



