428 STORAGE SYSTEM 



3. Storage for ecological purposes. 



Many seeds and fruits, and also certain leaves and flowers, accumu- 

 late stores of plastic material for purely ecological purposes; in such cases, 

 the reserve-materials which most frequently consist of carbohydrates, 

 but which may also include fats or protein-compounds are employed 

 to attract animals, the guests performing some useful office in return 

 for the food with which they are provided. Storage- tissues of this 

 kind may be termed feeding-tissues. 



The most prevalent type of feeding-tissue is exemplified by the 

 juicy pulp which forms so characteristic a feature of so many fruits 

 and pseudo-carps ; in all such cases the pulp is devoured by some 

 animal in most instances a bird while the seeds are either scattered 

 in the act of feeding, or subsequently ejected from the crop, or, finally, 

 voided with the excrement. These pulpy tissues are generally com- 

 posed of large thin-walled parenchymatous cells, with feebly developed 

 protoplasts and large sap-cavities. The attractive material most often 

 consists of one or more kinds of sugar {glucose, fructose), sometimes 

 also of starch (e.g. in Musa and Arlocarpus), or of oil (Oka, Persea 

 gratissima, Durio zibethinus). The attractiveness of the fruit or seed is 

 also frequently enhanced by bright coloration, due to the presence of 

 chromoplasts, or of anthocyanin dissolved in the cell-sap, and by the 

 development of a characteristic flavour or aroma which owes its 

 existence to the formation of various metabolic by-products. 



Oily storage-tissues are often developed in the special appendages 

 of seeds which are known as arils, caruncles and strophioles, or in per- 

 sistent floral organs subserving the same purpose, namely, the attraction 

 of ants for purposes of seed-dispersal ; the insects endeavour to carry 

 off the seeds to their nests, but abandon a number on the way, and 

 thus assist in the distribution of the plant. 201 Sernander unites all 

 such oily appendages under the comprehensive category of elaiosomes. 

 Among the commoner plants which have seeds provided with elaiosomes, 

 may be mentioned Lvzula Forsteri, L. pilosa, Allium triquetrum, Helle- 

 borus foetidus, Chclidonium majus, Corydalis spp., Viola odorata and 

 Melampyrmn pratense. 



Similar in character to the oily appendages of seeds, are the small 

 "food-bodies" borne by the leaves of certain myrmecophytes ; these 

 bodies afford a supply of food to the protective ants that regularly 

 inhabit the plants in question. 202 In Cecrop'w adenopus and C. peltata 

 (Trumpet-trees) the lower surface of each leaf-base is covered with a 

 dense coat of hairs ; interspersed among the hairs are numerous minute 

 ovoid or pear-shaped structures, the Miillerian bodies, which, according 

 to Schimper, consist essentially of a mass of parenchymatous cells 



