Chapter XX. 



What Seeds are and how they are Produced. 



if 



About I 50.000 different kinds of plants produce seeds. A 

 seed may be defined as a )'oung' plant and its reserve-food- 

 material enclosed within a normally protective layer. Some- 

 times the food-material is deposited beside or around the 

 plantlet, as in the seeds of Indian corn and wheat. Again the 

 food-material nia)' be collected in the plantlet itself, giving to 

 it a white, meaty appearance, and pumpkin and bean seeds are 

 of this structure. It is a mistake to say that plants grow from 

 the seed, or rather it is a half-truth, for the Cjuestion is whence 

 did the plantlet come that is already present in the seed and 

 needs only to renew its development when the seed germinates? 

 This can be answered in a word. Leaving out of considera- 

 tion some abnormal or peculiar conditions of development, it 

 may be said that all plantlets in seeds arise from eggs. The 

 next question is ^^•hence comes the q.^% from which the plantlet 

 in a seed de\-elops? The reply is, that the egg. as in all other in- 

 stances, is produced in the l)ody of a female plant, v^till an- 

 other question — where is one to look for the female plant of a 

 rose or willow, or any other seed-producing species? To this 

 inquiry the answer is. the female, like all other females in the 

 great series of terrestrial ])lants. de\elops from a spore. Again, 

 one in(|uires. where is the spore to be sought? To this is the 

 response that it is formed in the young ovule or rudimentary 

 seed, occurring as a more or less oval, cxlindrical or elongated 

 cell in the centre of the seed-rudiment. 



W hat then is the seed-rudiment? It is a spore-case which 

 produces at its centre the single, large, thin-walled spore. In 

 seed-plants such a spore is called an ciiibryo-sac and it may 

 easily be found by opening yoimg pine-seeds in cones not more 

 than twehc nioiUhs old. L'nlike the large-spores of the smaller 



