The individuality of the chromosomes and their serial arrangement, etc. 131 



observations for still other species of plants. In many of the above cases 

 the prochromosomes were not followed throughout the prophases of 

 somatic mitosis, but evidence was given that the chromatin units in the 

 resting nuclei do not exceed the number of chromosomes for the respective 

 species. 



The resting nuclei of many species, however, show a finely divided 

 reticulated chromatin. A study of the formation of the reticulum in the 

 telophases and its behavior in the prophases, however, has led in many 

 cases to the identification of so-called "unit reticula" derived from single 

 chromosomes. Boveri (1888 and 1904) found evidence for this view 

 in the lobed form of the nuclei of Ascaris. Among those who have con- 

 tributed positive evidence of the existence of unit reticula in plants are 

 Gregoire and Wygaerts (1904) for Trillium grandijlorum; Martins 

 Mano (1905) for Solatium tuberosum and Phaseolus vulgaris; Gregoire 

 (1906) for three species of Allium; Yamanouchi (1910) for Osmunda 

 cinnamomea; Stomps (1911) for Spinacia oleracea, and Overton (1911) 

 for Podophyllum peltatum. The evidence strongly suggests that such 

 reticula are present in all species whose nuclei possess a finely reticulated 

 structure during the resting condition. 



The direct growth of the chromatin knots which are present in resting 

 nuclei into chromosomes was observed by Huie (1897 and 1899), who 

 fed the tentacles of Drosera and compared the nuclei of the fed tentacles 

 with those in unfed tentacles and was able to recognize the successive 

 steps in the growth of the chromatin masses. Rosenberg (1909 b) repeated 

 Huie's experiments and confirmed the results and pointed out the bear- 

 ing of the phenomena on the prochromosome hypothesis. 



Evidence for the continuity of the chromosomes is found in their 

 persistence through interkinesis. It is generally conceded that in many 

 forms the chromosomes scarcely change their form in passing from the 

 heterotypic to the homoeotypic division. This fact was shown as early 

 as 1899 by Guignard. 



Observations on species whose chromosomes show specific and con- 

 stant differences in size and shape have furnished much evidence for 

 the independent existence of these bodies. Heteromorphism of the 

 chromosomes has been found in plants especially by the following in- 

 vestigators : Rosenberg (1904) for Listera ovata, ten large and twenty-two 

 small chromosomes; Strasburger (1882) for Funkia Sieboldiana, six large 

 and eighteen small chromosomes; Miyake (1905) for Galtonia candicans, 

 twelve large and four small individuals; Schaffner (1909) for Agave 

 virginica, four large, three smaller ringshaped and five smaller bivalent 



9* 



