1883.] Significance of Water Glands and Nectaries. 43 



where a well-defined epithem tissue is present, such tissue may- 

 serve as a resistance, put in, between the vascular bundle and the 

 free surface, so that the water should not mechanically run out, 

 but that a definite pressure should be required. In connection 

 with this subject one can but draw attention to the fact that the 

 difference between the glands of the Dicotyledons and Mono- 

 cotyledons is very remarkable, for there are in the comparative 

 study of the glands, no gradual stages from the one group to the 

 other, and in fact such a study seems to give some support to 

 the view which has sometimes been put forward that the Mono- 

 cotyledons and Dicotyledons are branches from a common ances- 

 tor, and that there is not a gradual ascent from the one family 

 to the other. 



I should also like to put forward here a view which has struck 

 me, but upon which I would prefer to lay no stress. Comparing 

 generally, the Dicotyledons with the Monocotyledons, it seems to 

 me that whereas the former are typically land-plants in their 

 habit, the latter on the other hand are of essentially an aquatic 

 nature. There are, I know, many exceptions to this statement, 

 but considering from a broad standpoint the Gramineae, the 

 Juncaceae, Butomaceae, Marantaceae, Zingibereaceae, Aroideae, 

 Palmae, and Orchidaceae, one finds that they, are either typically 

 water-plants or need for their growth a plentiful supply of moisture. 

 It is of interest also to note that in most of the Liliaceae we have 

 bulbs which are capable of storing up large quantities of water. 

 Co-related to this fact we find, that as far as we know at present, 

 we have in the Monocotyledons, glands of simple structure, and that 

 there is little or no resistance put in, between the vascular bundle 

 and the free surface. In Dicotyledons, on the other hand, we find, 

 speaking generally, well-developed glands, which are present too, in 

 plants where we should suppose that they were not needed, as in 

 Callitriche as described by Borodin 1 . In the glands of Dicotyledons 

 there is a very pronounced resistance to the escape of water, and a 

 greater root-pressure is required to bring about exudation. The 

 constituent cells of the plant tissue, are also rendered more turgid 

 in consequence of the increased pressure, and the water is, so to 

 speak, parted with much less freely. In Monocotyledons, where the 

 supply of water is fairly constant, these special precautions for 

 economizing water-supply are apparently not taken. With regard 

 to the liquid exuded, we know that while the majority of these 

 glands exude what is apparently only pure water, others exude 

 water containing salts in solution, the salts being for the most 

 part, carbonates of calcium and magnesium. Such salts must ob- 



1 Borodin, Bot. Zeit. 1869, p. 883, and 1870, p. 841. The organs of which 

 Trecul (Ann. de Sc. Nat. 1854) speaks, in Victoria regia, I was unable to observe. 



