PRESIDENTIAL ADDRESS. 731 



recent Mangroves teing preserved in this way. Seeds and embryos appear to be 

 so uniform on the whole that it is difficult to understand how they could have 

 passed through a viviparous phase in the later stages of their evolution. 



The viviparous Mangroves, on the other hand, are full of diversity in detail, 

 and these diflerences would surely have left a permanent mark had the course 

 pursued been in conformity with Mr. Guppy's very interesting suggestion. That 

 there is a rich field awaiting detailed investigation in connection with the 

 fascinating subjects opened up by Mr. Guppy will be admitted by most naturalists. 



In glancing bacL: at the early seed-structures one is struck with the complexity 

 of their organisation as compared with the relative simplicity of modern seeds. 

 The pollen-chamber, the large elaborate integument, and the complicated vascular 

 arrangements, so characteristic of the Pteridosperm seed, have for the most part 

 passed away, giving place to much simpler structures. Occasional exceptions no 

 doubt occur ; the seeds of Palms have remarkable integuments, whilst those of 

 Magnolia, some Aroids, Sapotacefe, &c. show an unusual development of vascular 

 tissue. Most a.stonishing of all perhaps is the integumental tracheal sheath which 

 closely invests the nucellus of Cassytha} Though evidence of their precise func- 

 tion be lacking, the fact that many of these structures belong to the tropical forest 

 makes closer knowledge desirable. For in these localities the conditions must 

 have long been relatively stable ; thus increasing the chance that the structures 

 referred to still perform their pristine functions. These and other cases like them 

 need elucidation, but to the broad statement that the seeds of recent Spermophytes 

 are organised on simple lines there can be no question. This reduction in com- 

 plexity may be accounted for on two grounds. In the first place fertilisation by 

 motile sperms has been replaced by fertilisation by pollen-tubes. Instead of sperms 

 being discharged into an internal water-chamber upon which the archegonia 

 abutted, the male cells ,ire carried through soft tissues to the egg in a plastic tube. 



In other spheres the like befalls. If primitive man had occasion to journey 

 from Baker Street to Waterloo, he penetrated the forest and then swam the river ; 

 to-day his descendants are projected from the one to the other with accuracy and 

 despatch in a subterranean passage. 



Just at what stage the improvisation of the pollen-chamber gave place to the 

 newer method we have no knowledge. Perhaps some information on this point 

 may emerge from Dr. Wielaud's exhaustive researchps into the extensive Yale 

 collections of American Cycadeoideas. For the Bennettiteae already show a sim- 

 plification of the seed in certain respects ; though, owing to the late stages of 

 development usually found in European examples, this point could not be cleared up. 



The other cause that must have played a prominent part in the simplification 

 of the seed was the association with it of other structures which relieved it of a 

 part of the original load of duties that fell to its lot. The dense heads of Ben- 

 nettiies show us this, and the same may be said of most Coniferous strobili. But the 

 Angiospermic ovary provides the best example of a special organ inclosing the seed 

 or ovule, affording it protection during the immature stages and also collecting the 

 pollen. The steps by which this came about remain hidden, and any discussion ot 

 the matter is of course premature. The carpels may have been derived from 

 reduced sporophylls or from portions of sporophylls that were more closely asso- 

 ciated with the seeds. The cupule of Lyginodendron is an organ rather suggestive 

 in this connection. One is tempted to compare it with a rudimentary ovary, 

 playing the serviceable part of a moist air-chamber for the seed during the earlier 

 stages of its development. 



However, the origin of the fruit and of the flower, with all its manifold organs, 

 must be left to the future : they form no part of our theme. Some day a happy 

 discovery will yield a clue, and the reproach that we are in entire ignorance of the 

 affinities of the dominant phylum will be removed. 



The history of the seed, as I read it from the imperfect and fragmentary data 

 that are available, has been a series of advances spread over long geological periods. 



' M. Mirande, 'Le ddvelop. et I'anat. d. Cassythacees,' Ann. d. Sc. Nat., 9° ser. 

 bot., torn, ii., 1905. 



