REPKODUCTION 457 



cause not only the development of the sporophyte from 

 the oosphere, but a considerable additional growth of the 

 archegonium, forming the calyptra. The same thing may be 

 noted in those Rhodophyceae which produce a bulky cysto- 

 carp. The stimulus is, however, most easily observed in 

 the Angiosperms, where it produces effects in several regions 

 of both gametophyte and sporophyte. The oospore is 

 excited to growth, and after a series of cell-divisions becomes 

 the embryo ; while the definitive nucleus of the embryo-sac 

 similarly inaugurates a series of divisions, ultimately giving 

 rise to the endosperm, and other parts of the ovule undergo 

 modification, so that the seed can shortly be recognised. 

 Parts of the flower also exhibit renewed growth and further 

 development, the carpels especially, though not exclusively, 

 showing an almost coincident enlargement, which often 

 attains considerable dimensions, so that a bulky structure 

 known as the fruit is produced. The new tissue is usually 

 ordinary parenchyma, and in most cases it becomes conspicu- 

 ously succulent and frequently strongly acid. The attain- 

 ment of its maximum development is followed by a process 

 technically known as ripening. This may take one of two 

 directions ; the tissue may become dry and woody, the cells 

 losing nearly all their water, and their walls becoming con- 

 verted into lignin. On the other hand the succulence may 

 persist and even increase ; in such cases the acidity fre- 

 quently becomes very much diminished and a considerable 

 quantity of sugar is formed. Other changes in the cells lead 

 to the appearance of various flavouring matters, and often 

 of substances that are aromatic. Fruits thus acquire special 

 characteristics of flavour and fragrance which they do not 

 possess while they are young. The chemical changes which 

 give rise to these peculiarities are very diverse, and cannot 

 be said to be fully understood at present. 



We have noticed that the asexual reproductive cell, 

 whether spore or gonidium, is generally found to remain 

 in a state of quiescence for some time after its formation. 

 The same thing is seen, though not so constantly, in the 



