• Volume 27, Issue 3

      March 1948,   pages  54-86

    • Erratum

      K L Khanna

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    • Studies in the genus Phytophthora—II

      K M Thomas T S Ramakrishnan

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      Isolates ofPhytophthora from castor,Agave, and breadfruit and authentic cultures ofP. parasitica, P. parasitica var.piperina andP. colocasiœ were studied in detail in single strain cultures and in paired cultures in different combinations.

      It was found that the isolates from the different hosts under study easily combined withP. parasitica, P. parasitica var.piperina andP. colocasiœ, forming oospores. These oospores are of the same type and fall within the range of size recorded forP. palmivora andP. parasitica. The criteria on which the species under investigation are classified are critically examined and it is found that no significant differences exist between them. The three species are able to grow at 35° C.

      The readiness with which these combine to form oospores shows their specific affinity. It is argued that all the three species should be combined into one and the nameP. colocasiœ is adopted for the emended species as it is the oldest.

    • Cytology ofCoccinia Indica W. & A. with reference to the behaviour of its sex-chromosomes

      A K Chakravorti

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      A study of the somatic mitosis ofCoccinia indica has shown that there are 24 chromosomes in the nuclei of both male and female plants, of which one pair is heteromorphic (XY) in the male and homomorphic (YY) in the female.

      The somatic metaphase spindle originates from the polar caps which appear as a result of the shrinkage of the prophase nucleus.

      During synizesis of the pollen mother cell the tapetal cells become binucleate. In certain cases the nuclear divisions are followed by cytokinesis. The two nuclei of the daughter cell again divide, and the later nuclear divisions may or may not be followed by wall formation.

      At diakinesis of the pollen mother cell 12 bivalents have been seen, of which one is heteromorphic and has been found to be attached to the nucleolus.

      A polar view of metaphase I shows 12 bivalents. One of these is decidedly bigger than the others and is the sex-chromosome pair (XY), whose identity could be followed during most of the later stages of meiosis.

      Various forms of abnormalities have been noted, among which cytomixis and the binucleate condition of the pollen mother cells appear to be the most common.

      Laggards have been found to be characteristic of the species. The lagging univalents organize micronuclei which subsequently divide along with the dyad nuclei, resulting in polyspory.

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