128 Causes and Course of Organic Evolution 



that paraheliotactic movement in sensitive and in more sluggish 

 plants is associated with the pulvinus of the leaves, and is 

 probably due to molecular changes in the aggregation bodies. 

 But much added observation and experiment are needed before 

 exact statements can be made. 



To sum up shortly the foregoing considerations, it may be 

 said that definite chromatin masses or plastids evolved in the 

 probable order: first, of leucoplasts or chemoenergids that are 

 chemotactic (or olfactory and gustatory in higher animals) 

 in function; secondy of helioplasts (chromoplasts and chloro- 

 plasts) or photoenergids, that may be red or green in most 

 plants, but seem to exist as colorless bodies in fungi, and pos- 

 sibly in animals; thirdy of geoplasts or geoenergids that have 

 been recognized in root cells of flowering plants but may be 

 much more widely distributed; fourth, of gyroplasts or gyro- 

 energids that we know only in their functional activity, not 

 in their morphological identity; fifth, of thigmoplasts or mech- 

 anoenergids that are in the same category as the last so far as 

 plants are concerned, but which in the touch bulbs or touch 

 corpuscles and in the auditory organs of higher animals seem 

 to find an expression; sixth of parahelioplasts or parahelio- 

 energids, which again are only known in their energizing results, 

 not as yet as definite structures. The hydrotactic sense finally 

 requires further elucidation. 



Now as the writer and also his former student Watson have 

 pointed out (6^: 336) the typical plastid — whether leucoplast 

 or chromoplast — is linked to the cell nucleus by fine chromatin 

 threads. Further in minute structure and in stainability the 

 plastids and the cell nucleus agree. But cells of the filamentous 

 Blue-green Algae show small bodies embedded in the peripheral 

 chromatophore wliich have been called "granules" by Zach- 

 arias, *'red granules" by Butschli, "cyanophycin granules" by 

 Borzi, and *'cyanoi)lasts" by Hegler. These according to some 

 of the above-named authors are connected with the evolving 

 central nuclear skein by fine threads. It is to be regretted 

 that we still have little precise information as to nuclear con- 

 ditions in the Tetrasporacese, the Mycoidacese, the Pleuro- 



