THE PROTOPLAST AS HOUSE-BUILDER 



25 



Photo l>y] 



FIG. 43. SNOWBERRY (Symphoricarpus racemosus). 



[E. Step. 



A plant allied to the IFoneysuckle, whose tiny pink flowers are succeeded by clusters of pure white berries. 

 "NORTH AMERICA. 



The round shape occurs in most cells at a certain stage (not the earliest 

 stage, when they are contiguous at all points), but in few cases, compara- 

 tively, is this shape retained. The pressure of contiguous cells as growth 

 continues again effects changes, so that we get octagons and twelve-sided 

 forms, and sometimes cells of no definable shape at all. This may be 

 simply illustrated by getting several balls of soft clay and uniting them 

 by gradual and uniform pressure. The fruit of the Snowberry (Symphori- 

 carpus racemosus, figs. 4'2, 43) and the leaf of the Common Pink (Dianthus 

 caryophyllus) offer interesting examples of cells retaining the spherical or 

 more correctly oval form. The pulp enclosed by the outer membrane 

 of the berry of the first-named plant, even when full grown, consists of a 

 vast number of minute shining white granules, each of which is a perfect 

 and almost spherical cell. 



The numberless departures from the rounded shape are not all due to 

 pressure, however. Some cells remain long and narrow through their whole 

 history, as those of the hairy seed-coat of the Cotton-plant, to which 

 reference has been made ; and others to wit, the hairs om the leaves of the 

 Virginia Stock (Malcolmia maritima) and the Hop (Humulus lupulus) are 

 curiously branched. Stellate or star-shaped cells are also met with, being 

 found in the stems of many aquatic plants ; their rays are seldom very 

 regularly placed, and they vary in length on the same individuals. The 

 stellate cells shown in fig. 4.4, which, however, are not those of an aquatic 

 5 



