224 STECKBECK— ON COMPARATIVE HISTOLOGY 



tion of the peripheral protoplasm. (2) Division of the vacuole into 

 numerous small vacuoles which all remain surrounded by a part of the 

 wall of the original \acuole. (3) A very significant diminution of the 

 volumes of the vacuoles. 



Bokorny (3, p. 427-473) who studied aggregation in a number of 

 plants, not including any of the sensitives, considered the aggregation 

 mass to be a proteid which separates from the protoplasm. As to the 

 biological significance of aggregation, this author ventures no explana- 

 tion. 



Loew and Bokorny (26, p. 614) refer to aggregation as an "echte 

 Lebensreaction ". 



Klemm (22, p. 395-420) studied the nature of the substances that 

 appear in the aggregation masses. Among the constituents are proteins, 

 fats and occasionally tannin. 



The irrito-contractile centers, especially the pulvini, of most of the 

 sensitives taken up in this imestigation, were examined for aggregation. 

 Each puh inus in its structure, as fully described by Sachs (40, p. 793) 

 shows a central vascular bundle cyHnder, around which a wide cortex 

 is present, the width of the cortex varying in the different sensitives. 

 It is noteworthy that the structure of the pulvini is very similar in both 

 Leguminosae and Oxalidaceae. 



If the pulvini are put into a strong fixing solution of iron or gold or 

 platinum chloride while the leaflets are expanded, the cortical cells of 

 the pulvini are granular in their contents, but indicate no definite masses. 

 It should be observed that it is difficult to fix pulvinar tissue without 

 getting aggregation in that the cutting of the leaflets to put into the fixing 

 solution acts as a stimulation and causes aggregation. 



When sections, taken from pulvini of such plants as Mimosa pudica 

 or Biophytiim sensUiviim, are examined under the microscope they 

 indicate rather clear shining globular masses in most of the cells of the 

 cortex. These masses occur throughout the entire cortex, but relatively 

 more abundantly on the ventral side of the pulvinus, that is they are 

 more abundant on the side away from the light. Each contracted 

 aggregation mass occupies %-3^ of the cavity of the cell. 



The aggregation masses can be studied to better advantage if certain 

 chemicals are applied. For this purpose the writer has found the 

 following to be helpful— gold chloride, platinic chloride, ferric chloride, 

 ammonium carbonate, caffeine, silver chloride and silver nitrate. Gold 

 chloride when applied in a 5% solution stains the masses a purplish 

 brown. 



