230 NATURAL HISTORY OF BHOMPSTON POND. 



staminate flowers. But perhaps more plentiful is Sparganium 

 ramosum (Branched Bur-reed). The flowers consist of the 

 more mumerous and upper small staminate heads and the 

 lower and larger pistillate heads. A portion of the peripheral 

 part of a transverse section of the stem of Juncus (Rush) is 

 shown in fig. 100. The single row of epidermal cells (a) have 

 their external cell walls greatly thickened, which, together 

 with the columns of stereome (b) and the sclerenchymatous 

 tissue (c) around the vascular bundle, all assist in giving the 

 plant its characteristic toughness and rigidity. A stoma (d), 

 bounded by two guard cells, allows air to pass into the 

 intercellular spaces between the cells of the assimilating 

 tissue (e). The vascular bundle containing the xylem (f) 

 and phloem (g), with its supporting sclerenchymatous 

 ring, is surrounded by a ring of much larger cells (h). The 

 pith (i) consists of very characteristic stellate cells, the 

 rays of which either join with others of the same level or 

 with others of a higher or lower level, giving a very 

 beautiful effect. 



Such observations as this essay contains seem to remind 

 one that here indeed is a struggle for existence. To a casual 

 observer this might be overlooked, as it requires much time 

 and patience to study, for instance, the tussles that occur 

 between the sun animalcule and a water-flea. It is, how- 

 ever, a comparatively easy matter to examine the forms of 

 life to be found in the stomach of a newt larva, or to watch 

 the Dytiscus larva and its prey ; while the struggles of Hydra 

 with one or other of the Entomostraca are common observa- 

 tions. 



In this connection it is important to notice the designs and 

 devices the animals and plants possess for their protection, 

 while many exhibit very obvious weapons of offence to still 

 further assist them in this struggle for life. Besides the use 

 of the plants in affording food material, protection, nesting 

 material, &c., for animals, there are other instances of the 

 inter-relationship between plant and animal life, such as the 

 symbiotic algae in Hydra. 



