144 Elementary Biology. 



are termed, are divided into two large groups, the Monocotyle- 

 dones and the Dicotyledones. As an example of the first 

 group we may take the lily or hyacinth ; as an example of 

 the second, the buttercup. The former we shall discuss in 

 this, the latter in the following, section. 



First of all, it may be well to point out several obvious 

 points of distinction between these two plants, which are 

 easily observed and appreciated on the basis of the know- 

 ledge of plant structure we have already gained. 



A section of a stem of Lilium shows what we know now 

 as fibro- vascular strands scattered apparently irregularly 

 through the fundamental tissue, whilst a similar section 

 through the stem of Ranunculus (buttercup) shows the 

 strands arranged concentrically round the centre, which is 

 either hollow or occupied by a mass of fundamental tissue 

 known as pith. Again, the strands in Lilium are crowded 

 towards the surface, whilst in Ranunculus there is a toler- 

 ably thick layer of cortex between the outer edge of the 

 strands and the epidermis. Further, when we examine the 

 ordinary foliage leaves the veins in Lilium are found to run 

 parallel to one another, whilst those in Ranunculus start at 

 various angles from a central midrib, and the veinlets branch 

 and anastomose, or form a network over the entire lamina. 

 Lastly, when we look at the cone or flower, we discover that 

 although the leaves composing it are very different in 

 colour, shape, and microscopic structure from the leaves 

 which go to form a fir cone or a Selaginella cone, yet they 

 are, broadly speaking, the same in general character in Lilium 

 and Ranunculus, but differ in their arrangement on the 

 cone-axis in these two types. In the lily they are obviously 

 arranged in circles of three each, whilst the outer leaves at 

 least in the buttercup are arranged in circles of five. These 

 flowers are therefore said to belong to the trimerous and 

 pentamerous types respectively. There are other points of 

 distinction between the two forms we have selected, but 

 these will be referred to later on. 



