THE PROTOPLAST AS HOUSE-BUILDER 



37 



Opuntias, that well-known genus of the Cactus .order to which the Prickly 

 Pear (0. valgaris) belongs. They are plentiful enough, too, in the leaf-stalk 

 of the Common Ivy (Hedera helix). Cells containing these composite fibres 

 are described as spiro-annular. 



Another modification of the true spiral is found in reticulated cells 

 (Lat. reticulum, a small net), where the bands of thickening are arranged 

 in a net-like manner on the interior of the primary walls. By this disposition 

 of the secondary deposit, little trenches are left at variable distances, which 

 appear under the microscope like more transparent lines. The Touch-me-Not 

 Balsam (Impatiens noli-tangere) and the Mistle- 

 toe (Viscum album?) furnish interesting exam- 

 ples of reticulated cells (fig. 57). 



" It is scarcely possible," says Dr. Carpenter 

 in his Vegetable Physiology and Botany, "to 

 observe the number of different forms result- 

 ing from the varied combinations of the simple 

 elements, each of them probably having its 

 peculiar function in the Vegetable economy, 

 without being struck with the simplicity of the 

 plan by which Creative Design has effected so 

 many marvels, as well as with the extreme 

 beauty and regularity of the structures which 

 are thus produced. The comparison of such 

 specimens of Nature's workmanship as the 

 meanest plant affords, with the most elaborate 

 results of human skill and ingenuity, serves 

 only to put to shame the boasted superiority 

 of man ; for whilst every additional power 

 which is applied to magnify the latter serves 

 but to exaggerate their defects and to display 

 new imperfections, the application of such to 

 organized tissues has only the effect of dis- 

 closing new beauties, and of bringing to light 

 the concealed intricacies of their structure." 



But it is time to pass from this subject. We trust that we have now 

 treated with sufficient fulness the more important facts connected with the 

 thickening of the primary cell-wall by means of secondary deposit ; and that 

 some definite idea has been conveyed of the manner in which cells though 

 not all cells are made strong and hard and capable of firm resistance. We 

 will now consider some of the other substances produced in vegetable cells 

 as the result of protoplasmic activity. 



In treating of the movements of protoplasm in Vallieneria, allusion was 

 made to the minute green corpuscles contained in the living matter of the 

 long grass-like leaves, and carried round with it in the cells. These little 



FIG. 60. CELLS FROM LEAF OF 

 Vallisneria spiralis. 



Showing chloroplasts (the oval bodies 

 in the protoplasm. 



