272 PHYSIOLOGICAL BOTANY. PART II. 



absorb the sap from the surrounding soil. But in many 

 cases there is no separate provision of albumen in a de- 

 tached form, but this material, or something like it, is 

 diffused through the substance of the cotyledons. 



(270.) Development of the Oruli: So soon as the 

 embryo makes its appearance it becomes a centre of 

 vital action, attracting the juices of the plant and be- 

 ginning an independent existence. It continues to 

 increase at the expense of its several envelopes, and in 

 the end constitutes the bulk of the seed. The seed 

 then consists of this body enveloped by a single skin 

 (the spermoderm, art. 109-), which is composed of the 

 debris of all the envelopes blended together, and in some 

 cases there is also superadded a store of albumen. 

 Those ovaries which are not fertilized soon wither up ; 

 but still it often happens that the ovaria containing 

 them do not perish. On the contrary in some fruits, 

 as in the cultivated varieties of the pine-apple, where the 

 ovules are universally abortive, the ovary is developed 

 into a fleshy pericarp ; although such is not the case with 

 the wild plants which possess ovules. The same is 

 true also of the bread-fruit. In some oranges whose 

 ovules happen to be abortive, the flavour of the fruit is 

 much improved ; but in- many plants, when the ovules 

 are abortive the ovary does not increase. In ovaria 

 which contain numerous ovules it often happens that 

 some only are fertilized ; and sometimes only one ovule 

 arrives at perfection, the rest being either starved for 

 want of sufficient nutriment, or choked by the more 

 rapid growth of that which becomes a perfect seed. 

 In the oak for example, five ovules out of six are con- 

 stantly abortive. In the horse-chestnut it seldom hap- 

 pens that more than one arrives at perfection, though the 

 pericarp originally contained six ; and though all of 

 them, for some time after their fertilization was se- 

 cured, had every appearance of health and vigour. In 

 the stone fruits plums, peaches, &c. we generally 

 find only one ripe kernel, though two ovules are 

 always present in the early stages of the fruit ; the 



