TRANSACTIONS OF SECTION K. 823 



a sporangial stalk — and the tej^umentary system is au outgrowtli of tlae sporangial 

 primordium of somewhat variable origin and development, whoso first function it 

 is to carry and store water for the embryo, and then also to serve as a food- 

 reservoir. The whole construction is adapted to the function claimed for it. The 

 well-develo])ed vascular system from the placenta traverses the funicle, but the 

 subsequent fate of the uucellus forbids its passing through this, and the needs in 

 respect of water (and what it carries) of the embryo and of the other further 

 developments that proceed in the embryo-sac are provided for by the production 

 of the tegumentary outgrowths into which the vascular system may, if necessary, 

 be continued and spread out. 



That the tegumentary covering has this function we have direct proof in its 

 penetration by haustoria, derived either from the embryo itself or from the embryo- 

 sac, which absorb from it water and Ibod for the developing embryo. These 

 haustoria appear to be much more elaborate and more widespread than has been 

 supposed, and a definite correlation has been established in many cases between 

 them and the integuments. The thicker the integument the hetter developed is 

 the haustorium. In some ovules where no vascular system appears in the 

 integument, the chalazal haustorium is prominent, and it can therefore at once tap 

 the main water-supply of the ovide. We know also of cellular ingrowths pro- 

 ceeding from the vicinity of the vascular system of the raphe to the interior of the 

 embryo-sac, and these, too, may have a conducting function. All these point to a 

 water and nutritive function in the integuments. The protective function of the 

 tegumentary system to which attention has heen chiefly directed must be primarily 

 only slight. It only becomes prominent as the seed is formed, and then changes 

 consonant therewith, and with its changed function, proceed within it. Nor can 

 we now, with our increased knowledge of the ways in which the pollen-tube may 

 reach the embryo-sac, consider the function of the integuments in forming the 

 micropylar canal as one of so much importance to the reproductive act as was 

 formerly supposed. We obtain, I thmk, a better conception of the ovule in the 

 view that the primary function of the tegumentary system is that of a water-jacket 

 and food-store, and that it has been developed in response to the special demands 

 for water involved in the seed-habit.^ 



To the question why there are two integuments in some cases and only one in 

 others we can only reply that our knowledge of ovular structure and changes is 

 yet too slight to permit of a definite opinion being expressed. We find that there 

 is a remarkable concurrence of the unitegminous ovule with a gamopetalous corolla 

 in the flower, for the character apparently holds for the whole of the gamopetalous 

 Dicotyledones excepting Primulales. On the other hand, not all Polypetalfe have 

 hitegminous ovules, whilst bitegmeny is usual in Monocotyledones. Recently the 

 character has been used by Van Tieghem as one of prominence in his new classifica- 

 tion of the families of Dicotyledones. But it is not so constant an one as his 

 groups of Unitegmineffi and Bitegminete woidd lead one to suppose. The 

 degree in which it is inconstant we cannot yet fix, because we know details of so 

 few genera. We do know, however, that all genera in one family are not always 

 alike in respect of it. In Ranunculaceje, for instance, the most of the genera with 

 radial flowers are unitegminous, whilst those with dorsiventral flowers are 

 bitegminous. Again, in Rosacese, the Potentillre are unitegminous, as is Rosa, 

 whilst PomesD and Pruneae are bitegminous ; and of the Spiraaere, Neillia is 

 unitegminous, but the closely allied Spirasa is bitegminous.- In other cases the 



' To discuss the morphological interpretations of the funicle and integument that 

 have been advanced would carry me beyond the scope of this address. I do not 

 know that an axial hypothesis for any part of the oviile is now maintained. The foliar 

 interpretation of the funicle and integuments as against their sporangial nature is 

 supported by two distinct schools of botanists. One approaches the subject from the 

 standpoint of the anaphytose of the earlier years of last century, and appeals largely 

 to teratology ; the other from that of vascular anatomy. I do not accept the 

 starting-point of either the one or the other. 



- Spiraea is, however, esalbuminous, whilst Neillia is albuminous. 



3h2 



