POLLEN FLORA OF PAKISTAN – LXVIII
Pollen morphology 20 species of the family Alliaceae from Pakistan has been examined by light and scanning electron microscope. Pollen grains are usually bilateral, hetropolar mostly boat shaped, sexine thicker tor thinner than nexine. Tectal surface is mostly rugulate foveolate or subpsilate rarely reticulate. On the basis of apertural types 3 distinct pollen types are recognized, viz., Allium fedtschenkoanum –type, Allium grifthianum-type and Allium roylei-type.
BIOLOGICAL VALUE AND MORPHOLOGICAL TRAITS OF POLLEN OF SELECTED GARLIC SPECIES ALLIUM L.
Summary This study was conducted in the years 1997 1999. From the collection of the UMCS Botanical Garden, nine species of garlic were selected (A. aflatunense, A. atropurpureum, A. caeruleum, A. cernuum, A. ledebourianum, A. lineare, A. sphaerocephalon, A. victorialis, A. ursinum) and one subspecies (A. scorodoprasum subsp. jajlae). Pollen grain viability was evaluated on microscopic slides stained with acetocarmine, germination abi lity on the agar medium and measurements of grains were made on glycerin jelly slides. The studied species were characterized by high pollen viability (87 99%) what indicates the great value of garlic flowers as a source of protein rich feed for honey bee and wild pollinating insects. Very low germination of pollen on the agar medium was recorded. The length of the equatorial lon gitudinal axis ranged from 24.3 µm to 37.5 µm and it allowed pollen of most garlic species to be classified as medium sized grains and only the pollen of A. caeruleum and A. cernuum was included in the group of small sized grains.
Lake Muzahi, Rwanda: limnological features and phytoplankton production
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NHinf4sup+-N can be high.Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m)In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.