In E. marginata 12 nonarticulated laticifer initials arise in the cotyledonary node of the young embryo during the early heart stage. The initials arise progressively in the developing embryo, the first laticifers differentiating simultaneously with or shortly before the elements of the pro‐cambium. The laticifers occupy a position lateral to the six procambial strands which are formed in the embryo. Upon subsequent growth each laticifer becomes vacuolated and nuclear division unaccompanied by cytokinesis results in the formation of a coenocytic protoplast. The enlarging laticifer produces several branches, one growing into the cotyledon, another growing down along the hypocotyl penetrating toward the root meristem, and one or several growing along intercellular spaces of adjacent cells. No fusion of these branches with one another or adjoining parenchyma cells was observed.

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Investigations were carried out on the effects of various combinations of sucrose and kinetin concentrations on growth and chlorophyll production in a green and a nongreen clone of pith callus of Nicotiana tabacum L. It was found that 2 milligrams per liter or higher amounts of kinetin induced greening in the nongreen tissue. The observations suggested that growth of the callus and synthesis of chlorophyll and soluble protein are controlled by relative concentrations of sucrose and kinetin in the medium. Kinetin was found to be inhibitory for chlorophyll synthesis in the green callus.The role of cytokinins as retardants of chlorophyll and protein degradation in senescing leaves is well documented (1,4,5,7, 10,(12)(13)(14)(15) Media Used. Media containing modified (6) Murashige and Skoog's salts and vitamins with various combinations of sucrose (0, 0.5, 1, 2, 4, 6, and 8%) and kinetin (0, 2, 4, 6, and 8 mg/liter) were used. These were gelled with 0.8% agar. Ten milliliters of the medium were pipetted into each culture tube (150 X 25 mm) and sterilized by autoclaving at 120 C and 15 psi for 20 min. In each tube 100 to 150 mg of callus were planted. This corresponded to 6 to 10 mg dry weight of green tissue or 4 to 6 mg dry weight of the nongreen tissue. The cultures were maintained at 26 + 1 C and under continuous illumination of 225 to 250 ft-c. Twelve cultures of each clone were maintained on the experimental media. At the time of inoculation the stock cultures were 4 to 5 weeks old and were growing exponentially.Collection of Data. Data on weight, soluble protein level, and amounts of chlorophyll a and chlorophyll b were collected. Amounts of protein and chlorophyll in stock cultures at the time of inoculation were determined (Table I). Preliminary experiments had shown that a minimum of 2 mg/liter kinetin was required to induce greening in the nongreen tissue. However, the green color persisted only for 2 to 3 weeks. Therefore, the data on the cultures from nongreen clone were collected twice: once, on six randomly selected samples, 1 week after greening was induced, and then on the remaining six cultures 4 weeks after the day of induction of greening. The day on which any of the cultures started turning green was regarded as the day of induction of greening on a particular medium. No data were collected on media on which none of the cultures turned green. The data on all 12 cultures from green clone were collected only once, 5 weeks after inoculation.Cultures of a batch were pooled together, and their total wet weight was determined. A sample was dried to determine the wet weight to dry weight ratio. For protein determination a known weight of callus was homogenized in 0.1 M phosphate buffer, pH 7.0, with a mortar and pestle. The homogenate was centrifuged at 18,000g for 10 min to remove the debris. Soluble protein was determined in the supernatant solution by the method of Lowry et al. (8). For chlorophyll extraction a known amount of the callus was homogenized in a 2:1 (v/v) mixture of methanol and ...

Interspecific hybrids from the crosses between Brassica campestris, B. carinata, B. juncea and B. napus were obtained through m vitro ovary and ovule culture. F 1 hybrids were studied morphologically and flow cytometry was used to estimate 2C nuclear DNA content both in parental Brassica species and their hybrids. It was found that in comparison with the A genome, the B and the C genomes of Brassica contained 26.9 % and 43.9 % more DNA, respectively. This finding may be used to distinguish interspecific hybrids containing various genome combinations. It was concluded that flow cytometric analysis of nuclear DNA content might be useful tool in Brassica breeding.

Investigations were carried out on the in vitro morphogenetic responses of inflorescence segments and gynoecia of several species of Haworthia (Liliaceae). Morphogenetic responses of explants were not species specific. It was found that coconut milk was essential for the growth and differentiation of Haworthia tissue if White's basal medium was used. However, growth and differentiation could be supported by a modified Murashige and Skoog's medium, without any supplements. The investigations demonstrated’ the importance of inositol and ammonium nitrogen in the nutrition of Haworthia tissue cultures. A chemical control of callusing and shoot and root differentiation was obtained by providing appropriate amounts of auxin and cytokinin in the culture medium.