396 MORPHOLOGY. 



No law can at present be laid down concerning the number of in- 

 teguments, except that, so far as my observation extends, all Monocoty- 

 ledons, without exception, possess two integuments, whilst in Dicotyledons 

 we find sometimes two, sometimes one, and sometimes none at all. 

 Speaking generally, we may say that in monopetalous plants the form- 

 ation of one, and in polypetalous two integuments, are the more frequent. 

 The total absence of integuments is the least frequent condition. 



In the RanunculacecB one and two integuments occur in the same 

 family ; and, as I believe, in the same genus Delphinium, of which most 

 species have two, but D. tricorne and chilense only one integument. 

 Otherwise, so far as my knowledge extends, the number of integuments 

 in the same family is a very constant character. A certain recognition 

 of the very earliest conditions of the seed-bud is a matter of great dif- 

 ficulty in some plants, easy as it is in others ; and the actual size of the 

 parts to be investigated is by no means the cause of this. One of the 

 smallest seed-buds and germens is, for example, presented by Urtica 

 dioica, and yet this is one of the cases in which it can be traced ; the 

 isolation of a germen, and a slight pressure with a glass plate, suffice to 

 make all clear. The difficulty is much more frequently caused by a 

 very dense (preventing transparency) or very loose (interfering with 

 certainty of the section) structure ; by the form of the seed-bud (as in 

 the Asclepiadacece) rendering the section of the seed-bud in symmetrical 

 halves difficult ; by the unsymmetrical arrangement, which renders the 

 precise section into two halves, an impossibility (for instance, in Ve- 

 ronica serpyllifolid} ; by the nature of the contents of the cellular tissue 

 destroying the transparency, and especially by the presence of much 

 hairy structure from which the air can scarcely be disengaged, which 

 makes observation impossible, and, even when the air is driven out, con- 

 fuses the appearances by the irregular superposition. We often hear 

 the following reasoning : " Since a matter could not be observed in such 

 and such larger parts of plants, it is unlikely that any one has ob- 

 served it in much smaller ones." My certain conclusion from this is, 

 that he who thus argues has made but very superficial ob- 

 servations. Taught by experience, I, on the contrary, now 

 frequently seek in preference the smaller plants, because 

 they are often the most advantageous for investigation on 

 account of needing no preparation. Water plants are es- 

 pecially to be recommended for most investigations, since 

 their usually watery and transparent parenchyma greatly 

 favours observation. These are unfortunately too little cul- 

 tivated in our botanical gardens. 



The common form of the papilla of the nucleus is that of 

 a roundish hemispherical body (fig. 239. m) ; sometimes it 

 is drawn out cylindrically, and then somewhat enlarged again 

 at its extremity, as, for example, in the naked nucleus of 

 Loranthus, where the point of the nucleus resembles a style 

 in form (fig. 243. g). 



Another point worthy of attention is the formation of the 

 micropyle : this is commonly only a simple canal, the length 

 of which is dependent merely upon the thickness of the integuments ; 

 sometimes, however, it is a large opening, from which the inner parts 



843 Loranthus Deppeanus. Part of the flower in longitudinal section, a, Pedicel , 

 c, embryo-sac ; o, n, floral envelopes and stamens, cut off; g, nuclear papilla, elongated 

 so as to resemble a style. 



