LECTURE XXV. 



SEED-PLANTS are divided into two great subdivisions. The first 

 comprises plants resembling the pine, and they bear their mega- 

 sporangia or ovules quite exposed so that the microspores may be 

 carried directly to the nucellus. In the second subdivision the 

 ovules are completely enclosed in a capsule formed by a single 

 megasporophyll (carpel) or by several megasporophylls cohering 

 together. In this case the pollen-grain itself does not reach the 

 ovule but is arrested by a special receptive portion of the carpel. 

 There it germinates and produces a tubular gametophyte for 

 traversing the tissue of the carpel as well as that of the nucellus. 

 The first subdivision is called the Gymnosperms ; the second, the 

 Angiosperms. 



To illustrate the salient features of these Angiosperms we select 

 two examples. The first of these is the Buttercup. Any kind 

 of Buttercup will serve our purpose, but perhaps Ranunculus 

 bulbosus or Ranunculus repens are the most easily obtained. 



The plant is herbaceous and its leaves, stems and roots are 

 easily recognised. In the case of R. bulbosus the upright stems 

 spring from a bulbous mass from the lower side of which many 

 cord-like roots grow. The larger green leaves, which are com- 

 paratively soft and hairy, are attached to the top of the bulb by 

 their somewhat hairy gutter-shaped stalks. The upright stems 

 bear smaller leaves with short widened stalks ; their branches 

 terminate in flowers. The leaves are subdivided into three leaflets 

 (pinnae) and these are further so deeply indented as to form leaflets 

 of a second order (pinnules). The leaf-stalk is continued upward 

 and forms a rachis connecting the pinnae together, and ribs on the 

 pinnae and pinnules run down and pass into the rachis. 



The upright stems are tapering cylinders. They are hollow and 

 tubular, as may be readily seen by cutting them across. The 

 wall of these tubular stems is a few millimetres thick, and is com- 

 posed of the fundamental tissue and of the vascular bundles. 

 When cut across the fundamental tissue appears a translucent 

 green, slightly darker towards the outside. Embedded in this are 



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