238 



GENERAL BIOLOGY 



chyma cells of the cortical and pith regions. Here the reserve starch 

 made by the leukoplasts is stored, as also are many other plant nutrients. 



Secretion cavities of various kinds carry oils and other products of 

 gland cells. 



Colenchyma cell walls, especially in seeds and fruits, contain much 

 cellulose. This means that collenchymal cells are supporting and storage 

 tissue as well as synthesis tissue. 



Fig. 141. Storage Tissues. 

 These are the parenchyma cells of the 

 cortical and pith regions of the plant ; the 

 cellulose in the collen chyma cells (which 

 makes collenchyma a synthesis, supporting, 

 and storage tissue), and cavities of stone 

 cells and fibers. 



A, grain of corn, cut lengthwise ; C, coty- 

 ledon ; E, endosperm ; H, hypocotyl ; P, 

 plumule. 



B, starch grains in the cells of a potato 

 tuber. 



Fig. 142. Reproductive Tissues. 

 Diagrammatic sections of sporogonia of 

 liverworts : A, Riccia, the whole capsule being 

 archesporium except the sterile wall layer ; 

 B, Marchantia, one half the capsule being 

 sterile, the archesporium restricted to the other 

 half ; D, Anthoceros, archesporium still more 

 restricted, being dome-shaped and capping a 

 central sterile tissue, the columella (col) 

 (After Goebel). 



Cavities of Stone cells and Fibers may contain nutrient material in 

 a few cases, but in such instances it is not readily available for the plant. 



Reproductive Tissue (Fig. 142). From inner tissues of anther and 

 ovary in flowering plants. 



When pollen is transferred from anther ( ) to 



stigma ( ) the process is called pollination. Wind, 



insects, and water are means by which pollen is carried from one plant 

 to another. Bees are common carriers, and the remarkable way some 

 plants are adapted to forcing any intruder to carry pollen with it, is one 

 of the most astounding of all adaptations in nature (Fig. 239). 



POLLINATION 



Pollination can probably best be understood by considering the mod- 

 ern pines. In the common Scotch Pine (Fig. 143), (Pinus silvestris) 

 the microsporophyls (called stamens in the flowering plants) are 

 massed into cones about 1 centimeter in length, and these cones are in 

 turn massed in clusters. 



There are two sporangia on the lower surface of each microsporo- 

 phyll. These microspores or pollen escape from the sporangia and are 

 carried by the wind (often for many miles) to the megaspore (carpellate) 

 cones. 



The megaspore cones grow singly or in clusters near the ends of the 

 upper twigs of the season's growth, and are also about one centimeter in 

 length. There is a general axis on which flat megasporophyls are borne. 

 Each of these megasporophyls bear two inverted megasporangia or 

 ovules (Fig. 144). 



