In this paper I have introduced one case of modification of articulation at the word-boundary, i. e. the assimilation, which regularly takes place in Dutch, but is impeded in Czech. In Dutch the assimilation of [s] in front of [j] is the result of coarticulation, applied in order to reduce the articulatory effort. It is, however, not an isolated phenomenon, but it is connected with the not clearly defined phonological and phonetic opposition of [s] and [š]. In Czech, despite the presumption that the coarticulation of the [s] in front of [j] also is possible, it is not audible for the speakers as modification, and - most importantly - it does not yield assimilation of the former to the latter, i. e. the realization of [š]. In our opinion the constraints are complex, in the first place we should point to the distinctive role of the /s/ and /š/ in the whole system. The perceptual segmentation in Czech, moreover, is ruled by the distribution of word-stress at the initial syllable of the word (after a pause); this brings about the hyperarticulation of the syllable, so that no need is felt to reduce the articulation. Because of the typological difference between Czech and Dutch, as respectively inflective and not-inflective languages, the phonetic phenomena at the word-end can be very significant and should be examined further.
Comparative scanning electron microscopical studies were carried out on Chonopeltis australis Boxshall, 1976 collected from different localities in the Orange-Vaal River System in South Africa and on material of Chonopeltis minutus Fryer, 1977 and Chonopeltis australissimus Fryer, 1977 on loan from the Albany Museum, Grahamstown. This elucidates the fine structure of morphological features, which are of taxonomic importance and illustrates the significance of the copulatory structures on the legs as a taxonomic tool. It was also concluded that C. australissimus is the same as C. minutus, with C. australissimus the junior synonym.
The effect of water stress on the gas exchange (CO2, H2O), distribution, water potential (T*), membrane permeability and chlorophyll content was studied in two maize hybrids, of the high and low drought tolerance, in the vegetative phase of growth. Diťferences in the responses to drought between both hybrids were clearly marked. After 5 d of drought the decrease in the net photosynthetic rate uptake and losses, transpiration rate (E) and increase of stomata resistance (r^ were greater in the drought-resistant hybrid than in the drought-susceptible one. On the contrary, after 10 or 15 d of drought, the decrease of and 'P in whole seedlings was greater in the susceptible hybrid than in the resistant one. Significant differences between hybrids were also observed in the accumulation of *'^C, the membrane permeability and the chlorophyll content. For all treatments the amount of carbon accumulation in roots of the resistant hybrid increased, while that of the susceptible one decreased. In the drought-resistant hybrid we observed a greater chlorophyll stability and a smaller damage of cell membranes than in the sensitive one.