180 BOTANY 



Bolles Lee, working with Paris quadrifolia, claimed that the 

 structure of plant and animal chromosomes is essentially the same. 

 He found that in the homotypic division of meiosis there was an 

 achromatic axis which at certain stages of division showed a peri- 

 axial spiral differentiation, connected by means of a spiral flange 

 (these flanges appeared as lateral processes) surrounded by an 

 achromatic membranous sheath. According to Lee, the essential 

 difference between plant and animal chromosomes lies in the fact 

 that the former occasionally show alveolation, and the axes of the 

 latter are always more solid. 



Another general view of chromosome structure is that the 

 achromoatic matrix encloses a number of discrete chromatic units, 

 the so-called chromomeres. At prophase these chromomeres unite 

 in more or less regular rows in the matrix, which is also a constant 

 element of chromosome structure. Sands has investigated the 

 chromosomes of Tradescantia virginica from this standpoint. His 

 description is limited to the structure displayed by the chromo- 

 somes of the pollen-mother cells at diakinesis, their arrangement 

 on the equatorial plate, and their structure at anaphase and early 

 telophase in both pollen-mother cells and somatic cells. The 

 acetocarmine method was employed. Sands considered that his 

 results support the view that the achromatic matrix forms 

 a foundation for a number of chromomeres. These chromomeres 

 are arranged irregularly within a linin cylinder. The surface of 

 this cylinder may be either smooth or irregular, according as the 

 chromomeres do or do not project beyond the periphery. 



More recently Sharp has reinvestigated this problem in a 

 number of different plants. The species used were Trillium grandi- 

 florum, Allium cepa, Podophyllum peltatum, Vicia faba and 

 Tradescantia virginica. Benda's fluid was mainly used for fixa- 

 tion. The observations were confined to the large somatic chromo- 

 somes of these plants. In all cases it was found that the chromo- 

 somes were composed of two principal morphological units, which 

 exhibited considerable differences in their affinity for stains during 

 late telophase, interphase and early prophase of mitosis. These 

 staining differences, however, are by no means so marked at late 

 prophase, metaphase, anaphase and early telophase. 



