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 niiclei 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) fonnd 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 grandiflorum; Martins 
Mano (1905) for Solanum tulerosum and Phaseolus vulgaris; Gregoire 
(1906) for three species of Allium; Yam.a.nouchi (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 conflrmed the results and pointed out the bear- 
ing of the phenomena on the prochromosome hypothesis. 
E\ddence 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 foUowing in- 
vestigators: Rosenberg (1904) for Listera ovata, ten large and twenty-two 
smaU chromosomes; Strasburger (1882) for Funkia Sieboldiana, six large 
and eighteen small chromosomes; Miyake (1905) for Galtonia eandicans, 
twelve large and four small individuals; Schaffner (1909) for Agave 
virginica, four large, three smaller ringshaped and five smaller bivalent 
9* 
