DICOTYLEDONS. 179 



a raceme, and putting on a cover glass, examine with a power of from 

 fifty to a hundred diameters. In the older stages it is best to treat with 

 potash, which will render the young flowers quite transparent. The 

 young flower (Fig. 95, A) is at first a little protuberance composed of 

 perfectly similar small cells filled with dense protoplasm. The first of the 

 floral leaves to appear are the sepals which very early arise as four little 

 buds surrounding the young flower axis (Fig. 95, A, B). The stamens 

 (<7, an.} next appear, being at first entirely similar to the young sepals. 

 The petals do not appear until the other parts of the flower have reached 

 some size, and the first tracheary tissue appears in the fibro- vascular 

 bundle of the flower stalk (D). The carpels are more or less united from 

 the first, and form at first a sort of shallow cup with the edges turned in 

 (Z>, gy.}. This cup rapidly elongates, and the cavity enlarges, becoming 

 completely closed at the top where the short style and stigma develop. 

 The ovules arise in two lines on the inner face of each carpel, and the 

 tissue which bears them (placenta) grows out into the cavity of the ovary 

 until the two placentae meet in the middle and form a partition completely 

 across the ovary (Fig. 95, H). 



The stamens soon show the differentiation into filament and anther, 

 but the former remains very short until immediately before the flowers 

 are ready to open. The anther develops four sporangia (pollen sacs), the 

 process being very similar to that in such pteridophytes as the club mosses. 

 Each sporangium (Fig. E, F] contains a central mass of spore mother 

 cells, and a wall of three layers of cells. The spore mother cells finally 

 separate, and the inner layer of the wall cells becomes absorbed much 

 as we saw in the fern, and the mass of mother cells thus floats free in the 

 cavity of the sporangium. Each one now divides in precisely the same 

 way as in the ferns and gymnosperms, into four pollen spores. The 

 anther opens as described for Erythronium. 



By carefully picking to pieces the young ovaries, ovules in all stages 

 of development may be found, and on account of their small size and 

 transparency, show beautifully their structure. Being perfectly trans- 

 parent, it is only necessary to mount them in water and cover. 



The young ovule (7, J) consists of a central, elongated body (nucellus), 

 having a single layer of cells enclosing a large central cell (the macrospore 

 or embryo sac) (sp.). The base of the nucellus is surrounded by two 

 circular ridges (i, n) of which the inner is at first higher than the outer 

 one, but later (K, JL), the latter grows up above it and completely conceals 

 it as well as the nucellus. One side of the ovule grows much faster than 

 the other, so that it is completely bent upon itself, and the opening 

 between the integuments is brought close to the base of the ovule (Fig. 



