STORING AND AERATING SYSTEMS. 235 
6. The Storing System. 
Since the plant does not immediately consume all the sub- 
stances which it takes up or forms, it must possess some 
arrangement whereby these substances may be stored for future 
use. The plant therefore develops receptacles for reserve 
Substances, in which it deposits the building materials. Such 
reserve receptacles are the seeds,’ fruits, rhizomes, tubes, bulbs 
and perennial roots; indeed, even the stem (especially the me- ~ 
dullary rays)’ can become a receptacle for reserve substances. 
The substances deposited in these organs are mostly solid; 
‘readily soluble substances (sugar, dextrin) are avoided, as a 
rule, by the plant. In the sugar-beet, however, the sugar is a 
reserve substance. They are either carbohydrates (starch, inulin, 
cellulose, for instance in the Phytelephas seed), fats (oil) or 
albuminous substances (gluten, aleurone); but water also is 
stored for the germinating plant (bulbs), or it is energeti- 
cally retained by the fully-developed plant (epidermal water- 
tissue). * 
v. The Aérating System. 
In the development of plants, the interchange of gases plays 
an important part. The plant consumes carbonic acid (and 
oxygen) from the atmosphere, and gives up to the latter oxygen 
(and carbonic acid), as well as aqueous vapor. In order to render 
possible this interchange of gases, cavities in the tissue are 
necessary. These collect the gases, and the canals, which serve 
respectively for their entrance and exit, convey them from with- 
out to the interior and inversely. 
For these reasons the plant is abundantly provided with 
intercellular spaces (Figs. 129, 127), especially in those parts 
’ The seeds have received appropriate anatomical treatment by Harz, 
‘* Landwirthschaftliche Samenkunde.” Berlin, 1885. 
* Malpighi, ‘‘ Anatomes plantarum idea” (1671), had already recog- 
nized the medullary rays as reserve receptacles, 
® All bulbs (Bulbus Scille) attract water abundantly, in consequence 
of the mucilage and sugar which they contain. 
* Westermaier. Pringheim’s Jahrb., xiv., 43. 
