70 MORPHOLOGICAL DEVELOPMENT. 



develop themselves, or else they continue to supply such 

 substance while the germs partially develop themselves before 

 their detachment. Among plants this constitutes one dis- 

 tinction between seeds and spores. Every seed contains a 

 store of food to serve the young plant during the first stages 

 of its independent life; and usually, too, before the seed is 

 detached, the young plant is so far advanced in structure, 

 that it bears to the attached stock of nutriment much the 

 same relation that the young fish bears to the appended yelk- 

 bag at the time of leaving the egg. Sometimes, indeed, the 

 development of chlorophyll gives the seed-leaves a bright 

 green, while the seed is still contained in the parent- 

 pod. This early organization of the phasnogam 

 must be supposed rudely to indicate the type out of which 

 the phagnogamic type arose. On the foregoing hypothesis, 

 the seed-leaves therefore represent the primordial fronds; 

 which, indeed, they simulate in their simple, cellular, un- 

 veined structures. And the question here to be asked is 

 do the different relations of the parts in young monocotyledons 

 and dicotyledons correspond with the different relations of 

 the primordial fronds, implied by the endogenous and the 

 exogenous modes of growth? We shall find that they do. 



Starting, as before, with the proliferous form shown in 

 Fig. Ill, it is clear that if the strength required for main- 

 taining the vertical attitude, is obtained by the rolling up of 

 the fronds, the primary frond will more and more conceal the 

 secondary frond within it. At the same time, the secondary 

 frond must continue to be dependent on the first for its nutri- 

 tion ; and, being produced within the first, must be prevented 

 by defective supply of light and air, from ever becoming syn- 

 chronous in its development with the first. Hence, this 

 infolding which -leads to the endogenous mode of growth, 

 implies that there must always continue such pre-eminence 

 of the first-formed frond or its representative, as to make the 

 germination monocotyledonous. Figs. Ill to 115, show the 

 transitional forms that would result from the infolding of 



