SPORES 



101 



Thus, organisms as they get larger and larger have a smaller 

 and smaller surface in proportion to their contents, and at 

 length a size is reached when the surface is too small to take 

 in enough oxygen or food for the bulky interior. When this 

 size is reached, reproduction generally takes place. 



In simple unicellular organisms the whole body is repro- 

 ductive. In an Amoeba, for instance, which is reproducing, 

 the nucleus first divides into two halves. The halves then 

 separate and move apart, and between the two a constriction 

 occurs in the protoplasmic body which, getting deeper and 

 deeper, ultimately separates the Amoeba into two Amoebae. 



When we were a soft amoeba, in ages past and gone, 

 Ere you were Queen of Sheba, or I King Solomon, 

 Alone and undivided, we lived a life of sloth, 

 Whatever you did, I did; one dinner served for both. 

 Anon came separation, by fission and divorce, 

 A lonely pseudopodium I wandered on my course. 



Spores 



The Amoeba divided into two equal parts, and neither can 

 be regarded as the parent of the other. The yeast cell also di- 

 vides, but unequally. 



A little bulge appears 

 on its spherical sur- 

 face, which grows big- 

 ger and then breaks 

 off. In this case the 

 larger cell may be re- 

 garded as the parent. 

 If yeast cells are 

 starved, the proto- 

 plasmic contents of 

 each cell divide into 

 four, and each of these 

 four new cells secretes 

 round it a thickened 



f 



a 



ppli-wqlf "should the Fig. 56. Yeast highly magnified, a-tz, successivo 

 cell wan. ^nouia tne ^^^f budding. (Darwin's ^/e7nc/i^.so//;ora«//.) 

 yeast dry up, these 



spherical spores escape and are blown about, and should tlu-y 

 reach a suitable medium they will soon turn into ordinary yeast 



SL 



II 



