270 ME. A. S. HOENE— A CONTRIBUTION TO 



more horizontal, extension. The undei'-marq-in of the inteorunient has now enclosed and 



QX.X vy^ i;xxw xx^i,v._ 



extended heyoiid the lower end of the nucellus, and its nppcr concave end forms the 

 floor of the micropyle. The ujoper portion of the integument, which Baillon styles an 

 obturator, is of considerable bulk and of an unusual type. It invests the upper surface 

 of the nucellus and forms the roof of the micropyle. It consists of cells arranged in 

 curved rows [intr), clearly shown in D, E, that have originated from the short rows 

 shown in G. This curvature is due to the growth-changes, which cause the rotation 

 of the nucellus. The nucellus is entirely free from the integument. Subsequent 

 growth-changes place the axis of the nucellus towards the vertical, and are more 

 concerned with the development of the lower portion of the ovule. 



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A complete series of stages in the development of the nucellus has been obtained. 

 When the ovule has reached the stasje shown in G, the nucellus alreadv consists of 



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several short axial rows of cells. Erom PI. 29, fig. 69 it is evident that the primary 

 archcsporial cells have divided to form primary parietal and sporogenous cells. In one 

 row further divisions have ensued, resulting in the formation of three parietal and two 

 sporogenous cells. The next stage was obtained in A. himalaica, where a linear row 

 of four mcgasporcs and a definite layer of parietal tissue had been formed. The 

 embryo-sac, in the case shown in fig. 70 (JJaponica), will evidently be formed from the 

 lowermost member of the linear row, being relatively deep-seated. Sometimes more 

 than one megaspore prepares to germinate, as in fig. 71 {A. japonica), megaspores of 

 adjacent rows ; and in fig. 72 (A, himalaica) a second megaspore is situated near the 



embryo-sac, which, in this case, appears to be the third cell of the row. During the 

 formation of tlie megaspores, the nucellus increases in bulk by division of the cells 

 foruiing the axial row^s. The epidermal cells also undergo division (fig. 70). The 

 embryo-sac develops in the normal manner. 



Vascular Slructure. 



w 



A reconstruction of the vascular system of the flower of A. Japonica was made 

 in wax from serial transverse sections of a particular flower. The vascular system of 

 this flower will now be described, and can be best followed by diagrams of transverse 

 sections (Text-fig. 7). Three bundles of diff"erent sizes are present in the pedicel (A) : 

 of these the largest (A, 1, 2, 3, 4) divides first to form two and ultimately five bundles 



(B, 1, 2^, 2, 3, 4); another (A, 5-6) divides once— one branch forms a principal bundle 

 (B, 5), the other (B, 6) extends towards the axis a little and divides into two small 

 branches (C), which extend outward again and join the principal bundles (C,5, 7) on 

 either side ; the third (A, 7) forms two principal bundles (t), E, 7, 7'). Budimentary axial 

 branches are formed from the other bundles evident in the pedicel (B, C, rud. ax) 



The principal bundles extend as far as the point of insertion of the ovule without 

 branching (E), and then each divides to form two or three smaller branches (G); four 

 of these leave the ovary— one to each petal (G,i)^),— the remainder form first an arc- 

 shaped group (II) and higher up a single bundle in the style. 



