This constantly increasing quantity of fluid swells the loosened cuticle out in the form of a delicate bladder, which soon burst and allow the nectar to appear on the surface. Evaporation is costantly going on, so that, if the plant is supplied trough its roots with an abundance of water, the cell wall separates a denser external, from a less dense internal syrup, and a continuation of the osmotic action keeps up the secretion of nectar for a considerable lenght of time. At times the evaporation predominates, and crystals of sugar may then been found upon the gland, in a dense uncrystallized syrup; at other times the secretion is so plentiful as to collect in drops which occasionally flow upon the surface of the leaf. Carefully washing the glandular surface with pure water always lessened its power of secretion, and, if repeated several times, so as to remove the last trace of sugar, completely prevented further activity. The addition of a small drop of syrup, however, always caused a renewal of the secretion, in glands which had been thus washed". Abbiamo voluto riportare tutto questo brano perché con chiarezza espone una delle opinioni oggidì dominanti intorno a una pretesa forza osmotica a cui sarebbe dovuta la espulsione nettarea dall’interno delle cellule in cui è contenuto il nettare: opinione che siamo ben lunge dal condividere e che anzi ci sembra contraria alla legge fisica della diosmosi bene intesa.
Quanto alla efficacia protettiva di queste glandole togliamo da TRELEASE i seguenti interessanti dettagli.
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