PHANEROGAMIA : FLOWERS. 431 



endless, Science in constant confusion and vacillation, so long as no 

 standard exists by which to estimate the correctness of this or that 

 opinion. Such a standard can only be found in the history of deve- 

 lopment. Organs which have like origin, like laws of development, are 

 alike ; organs of different origin, different. Forms in the perfect con- 

 dition, which may occur in any part, are no characters for the distinction 

 of organs ; but only characters for their sub-division. These are the 

 rules with which the history of development furnishes us, to define 

 every vegetable structure with certainty. But more is required for their 

 application than the meagre examination of a dried plant. 



The formation of the aril and pulp with succulent cellular tissue is 

 very frequent, and the occurrence of lignification is on the whole much 

 more rare in the development of the funiculus ; yet elegant spiral cells 

 occur in the funiculi of some species of Veronica, and the funiculus of 

 the species of Magnolia (which I have unfor- 

 tunately never had an opportunity t of examining) 268 

 is said to consist wholly of spiral-fibrous cells. 



In the perfect aril, which wholly surrounds the 

 seed-bud like an integument (fig. 268. .}, the 

 closed is commonly distinguished from the un- 

 closed : the former never occurs ; where an ac- 

 tually closed structure surrounds the seed, it is un- 

 doubtedly a layer of the seed-coats. In the species 

 of Passiflora particularly, it is always open above. 

 Whether all the^ structures named in 172, those 

 occurring in Evonymus and Myristica, as also those 

 in Solamim, belong here, I will not assert, since I 

 am still ignorant of the history of development.* 



173. In conclusion, we have yet to examine the changes which 

 take place in the germen. The germen grown to the fruit is styled 

 the pericarp (pericarpium). Besides the generally considerable 

 enlargement of the mass, which depends sometimes on the expan- 

 sion of the existing cells, and sometimes on the production of new 

 ones, we have to consider the following points : 



First, the changes in the external parts, since the pistil, as its 

 mass enlarges, often considerably alters in the conditions of its parts. 

 The style, in particular, is usually cast off or dried up as a part of 

 no further use; more rarely it goes on growing, and sometimes 

 acquires a disproportionate size, for instance, in many Geraniacea. 

 The germen also frequently now first produces projecting ridges, 

 warts, gibbosities, or thin membranous appendages (wings). 



The conditions of the interior of the germen now become im- 

 portant. As in the formation of the entire pistil and of the 

 seed-bud to fruit and seed, so, as it would appear, the development 



* We have received an essay from Planchon on the 'arillus (Comptes rendus, Dec. 

 1844), which, from the extract published in the Botanische Zeltung, and his other works, 

 awakens no especial confidence. He asserts particularly, that in Myristica and Euonymus 

 no arillus occurs, but an excrescence of the micropyle, which he calls an arillode. 



868 Passiflora alba. Longitudinal section of the seed. a, Funiculus and hilum ; 

 /, chalaza ; d, external, /, internal layer of the testa ; b, endosperm ; r, embryo ; r, raphe ; 

 *, aril. 



