The Scholander–Hammel pressure bomb has been used to measure ontogenetic and seasonal changes in π0 (the osmotic pressure of the symplasm at zero water potential), πp (the osmotic pressure of the symplasm at ‘incipient plasmolysis’), εmax (the bulk elastic modulus near maximum turgor), and a number of other water relations parameters in single leaves of Acer saccharum and several species of Populus and in shoots of Tsuga canadensis and Picea abies. In newly emerged leaves of Acer, Populus, and Picea, π0, πp, and εmax are all small but rise rapidly with leaf development. These parameters stabilize at a maximum value or slowly increase with progress in season. In Acer, εmax declines shortly before senescence. In developing leaves, the water content reaches a maximum before the soluble solutes; this accounts for the low values of π0 and πp.In Tsuga π0 cycles through an annual maximum in winter and a minimum in summer. These changes may correlate with frost hardiness.

No abstract

TYREE, M. T., M. E. MACGRECOR, A. PETROV, itnd M. I. UPENIEKS. 1978. A comparison of systematic errors between the Richards and Hammel methods of measuring tissue -water relations parameters. Can. J . Bot. 56: 2153-2161. The pressure bomb is being used to a much greater extent to measure some tissue -water relations parameters such as osmotic pressure, turgol-pressure. and cell wall elasticity. Recently, Richards has developed a faster pressure-bomb method of obtaining these and other parameters than the method used by Hammel and modified by 11s. In this paper. we compare the two methods and conclude that Richards' method should not be used when accu~xcy is deemed important. The Richards method usually overestimatesosmotic pressure by 0.2 MPa(= 2 bars)and sometimes by 0.8 MPa (= 8 bars). TYREE. M. T., M. E. MACGRECOR, A. PETROV et M. I. UPENIEKS. 1978. A comparison of systematic errors between the Richards and Hammel methods of measuring tissue -water relations parameters. Can. J. Bot. 56: 2153-2161. La bombe $ pression est utilisee de plus en plus pour rnesurer certains parametres ayant trait aux relations plante-eau, telles que la pression osmotique, la pression de turgescence et I'elasticite de la pzuoi cellulaire. Pour mesurer ces dernieres ainsi que d'autres pammetres. Richards a ricemment dkveloppe une methode de bombe i~ pression plus lapide que In methode utilisee par Hammel et modifiee par les auteurs. Dnns cet article. les auteurs comparent lesdeux methodes et concluent que celle de Richards ne doit pas itre utilisee lorsque la precision des mesures est importante. La methode de Richards surestime ktbituellement la pression osmotique de 0.2 MPa (= 2 bars) et parfois de0.8 MPa (= 8 bars).[~r a d u i t par le journal]

It is a common experience that mosquito larvae when they are brought into a laboratory to undergo their development, often fail to develop normally. At times a high mortality takes place, or the larvae lapse into a condition of suspended development continuing as larvae for months. The latter phase usually ends in death before pupation can take place. I have been puzzled to account for these manifestations for a very long time, and have conducted various experiments in the hope of discovering the cause. The general opinion on the matter, I think, is that there is “something wrong with the food supply,” but as a matter of fact larvae supplied with an ample diet often show the same state of affairs.

No abstract