Cytology of Hevea

I. A study has been made on the cytology of the following Hevea species: H. brasiliensis MUELL. ARG., H. Spruceana MuELL. ARG., H. guianensis AVBL. H. collina HUBER. and of two species-hybrids: H. Spruceana x brasiliensis and H. collina X brasiliensis. In connection with the description of the species-hybrids and with the great variation of characteristics in Hevea the value of the recent taxonomy of Hevea is discussed. 2. As far as possible the behaviour of the chromosomes in meiosis has been investigated. From early diplotene to diakinesis terminalis­ ation of chiasmata and a decrease of the number of chiasmata from 2-6 to 1-2 takes place. Terminalisation is not entirely complete, the one or two chiasmata in late diakinesis being terminal or inter­ stitial and even central (cross-shape). 3. The haploid number of chromosomes has been proved to be 18 in the pollen mother-cells of all the species and forms investigated. Countings were made in diakinesis, metaphase-I, anaphase-I, inter­ phase and metaphase-II, the total number amounting to more than hundred meiotic stages, leaving no room for any doubt. In metaphasc plates of somatic divisions in root tips 36 chromoso­ mes were found. 4. In some cultivated clones of Hevea brasiliensis showing partial or total male sterility, irregular meiosis takes place which is coupled with the occurrence of univalents and multivalents; of the latter trivalents are most common. The same irregularities were found in the hybrid of H. Spruceana X brasiliensis.