LECTURE XLIT. 



arises subsequently. The portion i surrounds the nucellus of the ovule as a closely 

 investing envelope formed of several layers of tissue, and narrows anteriorly into 

 a canal. This investment is called the Inlegtmieut, and the canal in it just referred 

 to, which thus leads from the exterior down to the nucellus of the ovule, is the 

 Microfivh'. 



It will be of further service for preliminary guidance if Fig. 436 E is com- 

 pared with the preceding. The ovule is here represented in a more advanced stage : 

 I is again the integument, now with closed micropyle, much larger, and closely 



investing the nucellus of the ovule k k 

 on all sides. Within the latter we now 

 find the part e : this is the embryo-sac 

 filled with endosperm — or, as we may 

 also say, the macrospore filled with 

 the prothallium. In this structure the 

 young plant, the embryo, arises in con- 

 sequence of fertilisation. To note it 

 by the way, the portion marked /;/, in 

 the form of an annular cushion sur- 

 rounding the base of the ovule, is that 

 which in the autumn surrounds the 

 whole ovule (or, better, what is then 

 the seed) in the form of a red succu- 

 lent investment. 



In this description, I have for 

 the time being made no reference to 

 fertiUsation itself, but have only de- 

 scribed the complex of organs which 

 co-opera'.e in that process : in like 

 manner it will, I think, be advantage- 

 ous if we look at the result of the 

 fertilisation, before describing the pro- 

 cesses themselves. This result is the 

 development of the ovule into the 

 seed, capable of germinating, the parts 

 of which must be understood before 

 a proper insight can be obtained into its origin and significance. This can be 

 accomplished with the aid of Fig. 437, which represents the germination of the seed 

 of the Stone Pine, with which the other Coniferae essentially agree. / is the seed 

 in longitudinal section, consisting of three parts ; i- the hard thick testa developed 

 from the integument of the ovule after fertilisation ; c is the so-called endosperm, or 

 further developed prothallium — the black line separating the testa and endosperm is 

 to be supposed to represent the membrane of the macrospore, or, what is the same 

 Üiing, the embryo-sac. Finally, we have lying in the middle of the endosperm the 

 young embryo : zv is its incipient root, c a whorl of leaves which, owing to an extremely 

 unhappy idea of the older botanists, it is still the custom to term cotyledons. This 

 again is an entirely meaningless word, which however unfortunately can now scarcely 



Fig. 436 — Tnxits bacrata. A male flower 

 (enlarged) : a the pol. en-sacs. B an anther 

 with the pollen-sacs opened, seen from below. 

 C portion of a leaf-.shoot, with a foliage-leaf 

 1^, from the axil of which springs the fen-.ale 

 flower ; j its scales ; sk its terminal ovule. D 

 longitudinal section of the 'ame (magnified) : 

 /integument; kk nucelius of the ovule; a- a 

 rudimentary axillary ovule. D longitudinal 

 section through an older ovule, before fertili- 

 sation : i integument ; kk nucellus ; e endo- 

 sperm; m arillus ; s enveloping leaves. 



