Francis E. Lloyd — 164 — Carnivorous Plants 



third layer) never show these changes. There would, therefore, seem 

 to be a difference of function of these layers, the innermost taking no 

 part in secretion. Under severe conditions caUing for active secretion, 

 the outer layer may display a certain degree of plasmolysis, the cells 

 recovering by drawing water from the second layer. Homes regards 

 this plasmolysis as a normal event, and attributes it to the concentra- 

 tion of the mucilage by rapid evaporation so that it becomes hyper- 

 tonic to the cell-sap. Though normal, it occurs infrequently in plants 

 under usual conditions. Such plasmolysis can cause directly the frag- 

 mentation of the vacuole, as shown by plasmolysis studies in general. 



Summarizing, it seems certain that the rate of secretion obeys 

 changes in the external conditions, quite apart from any responses to 

 irritability to chemical substances which are presented at and during 

 digestion. The changes described as aggregation under which these 

 can be subsumed are therefore not alone the result of stimulation in 

 the usual sense (mechanical, chemical). 



The purpose of Homes' final paper was to determine if during di- 

 gestion there is a specific activity of the glandular cells different from 

 that during secretion of mucilage. The same methods were used as 

 previously and the various behaviors of gland cells fed with raw egg 

 albumin compared with those from leaves without nourishment. We 

 recall that during secretion, according to its intensity, any one of four 

 types of condition above mentioned may be found, these types being 

 a) cells with one large vacuole, h) cells with many small round drop- 

 lets, c) cells with irregular droplets, and d) cells with a thick reticulum. 



"If now the glands are fed, at whatever state they may be at the moment, a first 

 rapid change will occur in the direction from A to D, or from B to D, but if they are al- 

 ready in the state D, no change will be apparent. Later, after the reticulimi stage has 

 been reached, a gradual concentration of the vacuole takes place till a single concentrated 

 vacuole is present in each glandular cell. Then this single vacuole becomes more and 

 more hydrated and finally a large diluted vacuole is present and persists till the end of the 

 digestion. Practically any type of vacuole present during digestion can thus be found in 

 a "resting" tentacle, and it is consequently impossible, by examining a single tentacle, to 

 tell if it is, was or is going to be in the process of digestion. 



"But the vacuolar changes revealed by the statistical study can also be related to the 

 intensity of the secretory process or even more generally to the exchange of water between 

 the gland and the external medium. The first change towards the reticulum expresses 

 the increase of secretion which takes place immediately after feeding; the later hydration 

 of the single vacuole indicates the decrease of secretion and the beginning of absorption. 



"Aggregation is thus not the characteristic result of 'excitation' in a carnivorous plant, 

 but simply the expression of any rapid change in the water content, as can happen during 

 secretion or absorption of a liquid." (Homes in ep.). 



Thus stands the problem at the present. We are impressed with 

 what appears to be a relatively simple cytological behavior of the 

 cytoplasm (not speaking for the moment of the nucleus) and by the phys- 

 iological complexities indicated by the behavior of the glands and 

 tentacles during the process of digestion during which there must be 

 secretion and escape of enzyme (even though they may be al- 

 ready present in the mucilage), acid or acids, a substance inhibiting 

 bacterial action (Goebel), perhaps an odorous principle, and a more 

 active secretion of mucilage which ceases at the end of digestion and 

 absorption. Meanwhile, absorption takes place. Simple as the cyto- 

 logical behavior may be, it is, I feel, not yet thoroughly understood. 



