LESS, xxx SPOROrilYLLS . 375 



B, a single microspore, showing bladder-like processes of outer coat, 

 and contents divided into small prothallial cell (a} and large cell (/'), 

 from which the pollen-tube arises. 



c, diagrammatic vertical section of female cone, showing axis with 

 female sporophylls (sp. ph. ? ) bearing megasporangia (ing. spg), each of 

 which contains a single megaspore (ing. sp): per, the scale-like perianth 

 leaves. 



D, diagrammatic vertical section of a megasporangium, showing 

 cellular coat (t}> and nucellus (ncl}, micropyle (inpy}, and megaspore 

 (ing. sp} : the latter contains the prothallus (prth} in which are two 

 ovaries, that to the left showing a large ovum (ov} and neck-cells, while 

 that to the right has given rise to an embryo (emb] which is in the 

 phyllula stage, and has sunk into the tissue of the prothallus by the 

 elongation of the long suspensor (spsr). 



A microspore (mi. sp} is seen in the micropyle sending off a pollen - 

 tube (/. t}, the end of which is applied to the necks of the two ovaries. 



E, diagrammatic vertical section of a seed, showing coat (/), micro- 

 pyle (inpy}, and endosperm (end], in which is embedded an embryo in 

 the phyllula stage, consisting of stem-rudiment (st), cotyledons (ct}, and 

 root (r). 



(A and B, altered from Strasburger ; D and E, altered from Sachs. ) 



liberated the protoplasm divides, as in Selaginella, into two 

 cells, a small one (a) the vestige of the male prothallus, and 

 a large one (b) which does not develop sperms, but under 

 favourable circumstances undergoes changes which will be 

 described presently. 



In the female cone (c) each sporophyll (carpel, sp. ph, 2 ) 

 bears on its upper or distal side two megasporangia (so-called 

 ovules, mg. spg) the structure of which is peculiar. Each 

 consists of a solid mass of small cells called the nucellus (v,ncl\ 

 attached by its proximal end to the sporophyll, and sur- 

 rounded by a wall or integument (/) also formed of a small- 

 celled tissue. The integument is in close contact with the 

 nucellus, but is perforated distally by an aperture, the 

 micropyle (mpy\ through which a small area of the nucellus 

 is exposed. 



Each megasporangium contains only a single megaspore 

 (embryo sac, c and D, mg. sp) in the form of a large ovoidal 

 body embedded in the tissue of the nucellus. It has at 



